Sorry, I suspect it's specific to whatever part of the OS supplies dialogues to save files, but I'm not sophisticated enough to know what that means.
Here's the journal:



Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: [1:14:0808/145734.092083:ERROR:data_channel.cc(44)] Accepting maxRetransmits = -1 for backwards compatibility
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: [1:14:0808/145734.092197:ERROR:data_channel.cc(49)] Accepting maxRetransmitTime = -1 for backwards compatibility
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: [1:1:0808/145734.297061:ERROR:webrtc_sdp.cc(412)] Failed to parse: "a=msid: ". Reason: Missing track ID in msid attribute.
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: [1:1:0808/145734.297423:ERROR:webrtc_sdp.cc(412)] Failed to parse: "a=msid: ". Reason: Missing track ID in msid attribute.
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: [1:1:0808/145734.297582:ERROR:webrtc_sdp.cc(412)] Failed to parse: "a=msid: ". Reason: Missing track ID in msid attribute.
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: [1:1:0808/145734.297750:ERROR:webrtc_sdp.cc(412)] Failed to parse: "a=msid: ". Reason: Missing track ID in msid attribute.
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: [1:1:0808/145734.297838:ERROR:rtc_peer_connection_handler.cc(2296)] Failed to create native session description. Type: offer SDP: v=0
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: o=- 7056755024856063948 2 IN IP4 127.0.0.1
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: s=-
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: t=0 0
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=group:BUNDLE 0
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=msid-semantic: WMS
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: m=application 9 UDP/TLS/RTP/SAVPF 119
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: c=IN IP4 0.0.0.0
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: b=AS:30
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=rtcp:9 IN IP4 0.0.0.0
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=ice-ufrag:XXX
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=ice-pwd:XXX
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=ice-options:trickle
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=fingerprint:sha-256 XXX
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=setup:actpass
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=mid:0
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=sendrecv
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=msid:
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=rtcp-mux
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=rtpmap:119 google-data/90000
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=ssrc:1531460167 cname:XXX
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=ssrc:1531460167 msid:-
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=ssrc:1531460167 mslabel:-
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: a=ssrc:1531460167 label:
Aug 08 14:57:34 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: [1:1:0808/145734.297888:ERROR:rtc_peer_connection_handler.cc(1215)] Failed to parse SessionDescription. a=msid:  Missing track ID in msid attribute.
Aug 08 14:58:44 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: # _g_io_module_get_default: Found default implementation gvfs (GDaemonVfs) for ‘gio-vfs’
Aug 08 14:58:44 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: # _g_io_module_get_default: Found default implementation dconf (DConfSettingsBackend) for ‘gsettings-backend’
Aug 08 14:58:44 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: # watch_fast: "/org/gnome/terminal/legacy/" (establishing: 0, active: 0)
Aug 08 14:58:44 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: # unwatch_fast: "/org/gnome/terminal/legacy/" (active: 0, establishing: 1)
Aug 08 14:58:44 T450s-high org.gnome.SettingsDaemon.MediaKeys.desktop[2678]: # watch_established: "/org/gnome/terminal/legacy/" (establishing: 0)
Aug 08 14:58:52 T450s-high /usr/lib/gdm3/gdm-x-session[2412]: [dix] EventToCore: Not implemented yet
Aug 08 14:58:53 T450s-high /usr/lib/gdm3/gdm-x-session[2412]: [dix] EventToCore: Not implemented yet