I seem to have the same issue, though it seems to be triggered by the initial Docky instance crashing on startup. Details below:

$ /usr/bin/docky&
[1] 142970
[Info  11:50:46.372] Docky version: 2.2.1.1 Release
[Info  11:50:46.375] Kernel version: 4.19.28.2
[Info  11:50:46.375] CLR version: 4.0.30319.42000
[Error 11:50:46.487] [SystemService] Could not initialize power manager dbus: 'Could not load type 'Docky.Services.SystemService\+IUPowerProxy' from assembly 'DBus.Proxies, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' because it is implements the inaccessible interface 'Docky.Services.SystemService+IUPower'.'
[Info  11:50:46.488] [SystemService]   at System.Reflection.Emit.TypeBuilder.CreateTypeInfo () [0x002d6] in <d0e12f672b88444ab4b6d9b2ecf20142>:0 
  at System.Reflection.Emit.TypeBuilder.CreateType () [0x00000] in <d0e12f672b88444ab4b6d9b2ecf20142>:0 
  at DBus.TypeImplementer.GetImplementation (System.Type declType) [0x000e3] in <91cfe10d2aa049c9af550645dbbec075>:0 
  at DBus.BusObject.GetObject (DBus.Connection conn, System.String bus_name, DBus.ObjectPath object_path, System.Type declType) [0x00001] in <91cfe10d2aa049c9af550645dbbec075>:0 
  at DBus.Connection.GetObject (System.Type type, System.String bus_name, DBus.ObjectPath path) [0x0002b] in <91cfe10d2aa049c9af550645dbbec075>:0 
  at DBus.Connection.GetObject[T] (System.String bus_name, DBus.ObjectPath path) [0x00001] in <91cfe10d2aa049c9af550645dbbec075>:0 
  at Docky.Services.SystemService.InitializeBattery () [0x00030] in <2eddf23b3bc241c5a84ba4fe5c97ed0a>:0 
[Error 11:50:46.492] [SystemService] Could not initialize Network Manager dbus: 'Could not load type 'Docky.Services.SystemService\+INetworkManagerProxy' from assembly 'DBus.Proxies, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' because it is implements the inaccessible interface 'Docky.Services.SystemService+INetworkManager'.'
[Info  11:50:46.492] [SystemService]   at System.Reflection.Emit.TypeBuilder.CreateTypeInfo () [0x002d6] in <d0e12f672b88444ab4b6d9b2ecf20142>:0 
  at System.Reflection.Emit.TypeBuilder.CreateType () [0x00000] in <d0e12f672b88444ab4b6d9b2ecf20142>:0 
  at DBus.TypeImplementer.GetImplementation (System.Type declType) [0x000e3] in <91cfe10d2aa049c9af550645dbbec075>:0 
  at DBus.BusObject.GetObject (DBus.Connection conn, System.String bus_name, DBus.ObjectPath object_path, System.Type declType) [0x00001] in <91cfe10d2aa049c9af550645dbbec075>:0 
  at DBus.Connection.GetObject (System.Type type, System.String bus_name, DBus.ObjectPath path) [0x0002b] in <91cfe10d2aa049c9af550645dbbec075>:0 
  at DBus.Connection.GetObject[T] (System.String bus_name, DBus.ObjectPath path) [0x00001] in <91cfe10d2aa049c9af550645dbbec075>:0 
  at Docky.Services.SystemService.InitializeNetworkManager () [0x0005c] in <2eddf23b3bc241c5a84ba4fe5c97ed0a>:0 
[Info  11:50:46.502] [ThemeService] Setting theme: Air
[Warn  11:50:46.515] [DesktopItemService] Could not find remap file '/usr/local/[REDACTED]/.local/share/docky/remaps.ini'!
[Info  11:50:46.609] [DockServices] Dock services initialized.
[Info  11:50:46.729] [PluginManager] Loaded "Trash".
Cairo.Surface is leaking, programmer is missing a call to Dispose
Set MONO_CAIRO_DEBUG_DISPOSE to track allocation traces
Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
System.NullReferenceException: Object reference not set to an instance of an object
  at System.Collections.Generic.LargeArrayBuilder`1[T].GetBuffer (System.Int32 index) [0x00022] in <13c0993ff82548209b09f271bd5e6a78>:0 
  at System.Collections.Generic.LargeArrayBuilder`1[T].CopyTo (System.Collections.Generic.CopyPosition position, T[] array, System.Int32 arrayIndex, System.Int32 count) [0x00041] in <13c0993ff82548209b09f271bd5e6a78>:0 
  at System.Collections.Generic.SparseArrayBuilder`1[T].CopyTo (T[] array, System.Int32 arrayIndex, System.Int32 count) [0x0009a] in <13c0993ff82548209b09f271bd5e6a78>:0 
  at System.Collections.Generic.SparseArrayBuilder`1[T].ToArray () [0x00028] in <13c0993ff82548209b09f271bd5e6a78>:0 
  at System.Linq.Enumerable+Concat2Iterator`1[TSource].ToArray () [0x00024] in <13c0993ff82548209b09f271bd5e6a78>:0 
  at System.Linq.Enumerable.ToArray[TSource] (System.Collections.Generic.IEnumerable`1[T] source) [0x00021] in <13c0993ff82548209b09f271bd5e6a78>:0 
  at Docky.Items.AbstractDockItemProvider.set_Items (System.Collections.Generic.IEnumerable`1[T] value) [0x000f4] in <d76df703e9694236b146776d22b188cd>:0 
  at Docky.Items.FileApplicationProvider.RemoveTransientItems (System.Collections.Generic.IEnumerable`1[T] items) [0x00056] in <d76df703e9694236b146776d22b188cd>:0 
  at Docky.Items.FileApplicationProvider.UpdateTransientItems () [0x00228] in <d76df703e9694236b146776d22b188cd>:0 
  at Docky.Items.FileApplicationProvider+<WnckScreenDefaultWindowOpened>c__AnonStorey1.<>m__0 () [0x00026] in <d76df703e9694236b146776d22b188cd>:0 
  at GLib.Timeout+TimeoutProxy.Handler (System.IntPtr data) [0x0003c] in <5a439e0caae7469886e7119d9f6bc621>:0 
  at GLib.ExceptionManager.RaiseUnhandledException (System.Exception e, System.Boolean is_terminal) [0x00000] in <5a439e0caae7469886e7119d9f6bc621>:0 
  at GLib.Timeout+TimeoutProxy.Handler (System.IntPtr data) [0x00000] in <5a439e0caae7469886e7119d9f6bc621>:0 
  at Gtk.Application.gtk_main () [0x00000] in <7a41aae9f05e45b7b5a8cedfab67f8ff>:0 
  at Gtk.Application.Run () [0x00000] in <7a41aae9f05e45b7b5a8cedfab67f8ff>:0 
  at Docky.Docky.Main (System.String[] args) [0x00000] in <8d1179ef49784bf4bf25249afb56deb9>:0