It seems like I experienced a similiar error with Ubuntu 17.04 (with i5 3400 and RX 480). I wanted to re-login after the screen was locked. For more than a minute, I could not move the mouse nor switch from x environment to terminal or something like this. After some time, everything just worked fine again.

First, the following appears some times:
Aug 25 14:33:31 reichelt-desktop kernel: [14558.796706]  failed to send message 146 ret is 0 
Aug 25 14:33:31 reichelt-desktop kernel: [14559.219339]
Aug 25 14:33:31 reichelt-desktop kernel: [14559.219339]  failed to send pre message 5d ret is 0 
Aug 25 14:33:31 reichelt-desktop kernel: [14559.642303]
Aug 25 14:33:31 reichelt-desktop kernel: [14559.642303]  failed to send message 5d ret is 0 
Aug 25 14:33:32 reichelt-desktop kernel: [14560.066004]
Aug 25 14:33:32 reichelt-desktop kernel: [14560.066004]  failed to send pre message 148 ret is 0 

and than a similiar error occured:

Aug 25 14:33:35 reichelt-desktop compiz[2749]: ERROR 2017-08-25 14:33:35 unitynding->source != null <unknown>:0 g_value_set_object: assertion 'g_value_type_compatible (G_OBJECT_TYPE (v_object), G_VALUE_TYPE (value))' failed
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: Failed to fetch xid: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop compiz[2749]: WARN  2017-08-25 14:33:35 unity <unknown>:0 Failed to fetch xid: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: Failed to fetch type: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop acpid: input device has been disconnected, fd 16
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: Failed to fetch monitor: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop compiz[2749]: WARN  2017-08-25 14:33:35 unity <unknown>:0 Failed to fetch type: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: Failed to fetch maximized state: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: Failed to fetch xid: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop compiz[2749]: WARN  2017-08-25 14:33:35 unity <unknown>:0 Failed to fetch monitor: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: Failed to fetch xid: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: Failed to fetch property `_GTK_UNIQUE_BUS_NAME': GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: Failed to fetch path: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop compiz[2749]: WARN  2017-08-25 14:33:35 unity <unknown>:0 Failed to fetch maximized state: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: Failed to fetch xid: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop compiz[2749]: WARN  2017-08-25 14:33:35 unity <unknown>:0 Failed to fetch xid: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop compiz[2749]: message repeated 6 times: [ WARN  2017-08-25 14:33:35 unity <unknown>:0 Failed to fetch xid: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636]
Aug 25 14:33:35 reichelt-desktop unity-panel-ser[2771]: menus_destroyed: assertion 'IS_WINDOW_MENU(wm)' failed
Aug 25 14:33:35 reichelt-desktop compiz[2749]: WARN  2017-08-25 14:33:35 unity <unknown>:0 Failed to fetch xid: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636
Aug 25 14:33:35 reichelt-desktop kernel: [14563.397640] usb 2-1.1: new low-speed USB device number 5 using ehci-pci
Aug 25 14:33:35 reichelt-desktop kernel: [14563.517356] usb 2-1.1: New USB device found, idVendor=046a, idProduct=0023
Aug 25 14:33:35 reichelt-desktop kernel: [14563.517360] usb 2-1.1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
Aug 25 14:33:35 reichelt-desktop compiz[2749]: message repeated 3 times: [ WARN  2017-08-25 14:33:35 unity <unknown>:0 Failed to fetch xid: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Keine derartige Schnittstelle »org.ayatana.bamf.window« des Objekts im Pfad /org/ayatana/bamf/window/35651636]
Aug 25 14:33:35 reichelt-desktop mtp-probe: checking bus 2, device 5: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.1"
Aug 25 14:33:35 reichelt-desktop mtp-probe: bus: 2, device: 5 was not an MTP device
Aug 25 14:33:35 reichelt-desktop kernel: [14563.527560] input: HID 046a:0023 as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.1/2-1.1:1.0/0003:046A:0023.0004/input/input22
Aug 25 14:33:35 reichelt-desktop kernel: [14563.585998] cherry 0003:046A:0023.0004: input,hidraw0: USB HID v1.11 Keyboard [HID 046a:0023] on usb-0000:00:1d.0-1.1/input0
Aug 25 14:33:35 reichelt-desktop kernel: [14563.595771] input: HID 046a:0023 as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.1/2-1.1:1.1/0003:046A:0023.0005/input/input23
Aug 25 14:33:35 reichelt-desktop kernel: [14563.653693] cherry 0003:046A:0023.0005: input,hidraw1: USB HID v1.11 Device [HID 046a:0023] on usb-0000:00:1d.0-1.1/input1
Aug 25 14:33:35 reichelt-desktop kernel: [14563.654103] usb 2-1.2: USB disconnect, device number 4
Aug 25 14:33:36 reichelt-desktop kernel: [14563.877606] usb 2-1.2: new low-speed USB device number 6 using ehci-pci
Aug 25 14:33:36 reichelt-desktop kernel: [14563.994060] usb 2-1.2: New USB device found, idVendor=045e, idProduct=0084
Aug 25 14:33:36 reichelt-desktop kernel: [14563.994064] usb 2-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
Aug 25 14:33:36 reichelt-desktop kernel: [14563.994067] usb 2-1.2: Product: Basic Optical Mouse
Aug 25 14:33:36 reichelt-desktop kernel: [14563.994069] usb 2-1.2: Manufacturer: Microsoft
Aug 25 14:33:36 reichelt-desktop kernel: [14563.997823] input: Microsoft Basic Optical Mouse as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.2/2-1.2:1.0/0003:045E:0084.0006/input/input24
Aug 25 14:33:36 reichelt-desktop kernel: [14563.997992] hid-generic 0003:045E:0084.0006: input,hidraw2: USB HID v1.10 Mouse [Microsoft Basic Optical Mouse] on usb-0000:00:1d.0-1.2/input0
Aug 25 14:33:36 reichelt-desktop mtp-probe: checking bus 2, device 6: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.2"
Aug 25 14:33:36 reichelt-desktop mtp-probe: bus: 2, device: 6 was not an MTP device
Aug 25 14:33:38 reichelt-desktop avahi-daemon[977]: Registering new address record for 2a02:810a:12c0:4e6c:35d5:a593:3500:9e5b on enp2s0.*.
Aug 25 14:33:38 reichelt-desktop avahi-daemon[977]: Withdrawing address record for 2a02:810a:12c0:4e6c:35d5:a593:3500:9e5b on enp2s0.
Aug 25 14:33:42 reichelt-desktop avahi-daemon[977]: Registering new address record for 2a02:810a:12c0:4e6c:35d5:a593:3500:9e5b on enp2s0.*.
Aug 25 14:33:42 reichelt-desktop avahi-daemon[977]: Withdrawing address record for 2a02:810a:12c0:4e6c:35d5:a593:3500:9e5b on enp2s0.
Aug 25 14:33:43 reichelt-desktop compiz: pam_ecryptfs: seteuid error
Aug 25 14:33:43 reichelt-desktop unity-panel-ser[2771]: menus_destroyed: assertion 'IS_WINDOW_MENU(wm)' failed
Aug 25 14:33:43 reichelt-desktop compiz[2749]: WARN  2017-08-25 14:33:43 unity.glib.dbus.proxy GLibDBusProxy.cpp:487 Calling method "EmitEvent" on object path: "/com/ubuntu/Upstart" failed: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name com.canonical.Unity.Test.Upstart was not provided by any .service files
Aug 25 14:33:43 reichelt-desktop systemd[2163]: Stopped target A target that, when running, represents the screen being locked.
Aug 25 14:33:43 reichelt-desktop systemd[2163]: Stopping Backing Service for the Unity Panel in Lockscreen mode...
Aug 25 14:33:43 reichelt-desktop unity-panel-ser[2771]: menus_destroyed: assertion 'IS_WINDOW_MENU(wm)' failed

I could not find ~/.cache/indicator-applet.log or some other ayatana-related stuff, so I can not provide additional information currently.