4.0 regression: Qt refuses to embed X11 video

Just took a checkout of the latest master -> 4.0.0-dev-11909-ga7dd702b

Platform: Ubuntu 18.04

Reproduce:

1. Play any video file. The video starts in another window.
2. Close the window from the cross (top).

Can't replay the video. The track progress bar keep moving despite clicking stop. App hangs. Have to restart.

I get these logs in the terminal ->

[0000561c03f5a370] qt interface debug: on_player_track_list_changed
[0000561c03f5a370] qt interface debug: on_player_track_list_changed
[0000561c03f5a370] qt interface debug: on_player_state_changed VLC_PLAYER_STATE_STARTED
[h264 @ 0x7f9b8010c6a0] nal_unit_type: 1, nal_ref_idc: 0
[0000561c03f5a370] qt interface debug: on_player_track_list_changed (video)
[0000561c03f5a370] qt interface debug: on_player_track_list_changed (audio)
[0000561c03f5a370] qt interface debug: on_player_state_changed VLC_PLAYER_STATE_PLAYING
[0000561c03f5a370] qt interface debug: on_player_track_list_changed (video)
[0000561c03f5a370] qt interface debug: on_player_track_list_changed (audio)
[00007f9b640c7e40] xcb_window window error: X server failure
[00007f9be4e7a110] upnp services discovery warning: search timeout
[00007f9be4e7a110] upnp services discovery warning: search timeout
[0000561c03f5a370] qt interface debug: on_player_state_changed
[0000561c03f5a370] qt interface debug: on_player_state_changed VLC_PLAYER_STATE_STOPPING
[h264 @ 0x7f9b800a83e0] nal_unit_type: 1, nal_ref_idc: 2
[00007f9b80072520] main decoder debug: killing decoder fourcc `h264'
[00007f9b80072520] main decoder debug: removing module "avcodec"
[0000561c03f439e0] pulse audio output debug: underflow

Notable:

xcb_window window error: X server failure

I compiled the latest vlc 3.0 branch. Not getting any error of this kind.

Will try to see if I can help on this.