Initial discussion here:
https://github.com/mixxxdj/mixxx/pull/2016
"What's going on is m_pCurrentTrack is null at construction time. When a track is loaded, some of the signals are crossed so that onMarkChanged is getting called before slotLoadingTrack is called. Therefore, once any track loads correctly, m_pCurrentTrack will never be null again so the crash is avoided. But also, I suspect onMarkChanged is always getting called for the old track, not the current one. onMarkChanged seems to be called by pmark->connectSamplePositionChanged signal. I'm not sure what event is triggering the sample position changes though."
"ok so this only occurs on tracks where a loop has been defined. So here are the reproduce instrux:
Start mixxx fresh
Load a track that already has a loop defined
crash
The trigger to the crash is basetrackplayer.cpp where it calls m_pLoopInPoint->set(loopStart); -- setting the loop start position triggers the sample position changed signal early, before the track pointer in woverview.cpp has been updated yet. It may just be enough to put a nullptr check around the access of m_pCurrentTrack in woverview.cpp, but I'm trying to figure out if there are any bad side effects to this misordering."
(https://github.com/mixxxdj/mixxx/blob/master/src/mixer/basetrackplayer.cpp#L188)
"Yes, It only happens with the LateNight skin. All of the other Skins are fine."
For me, putting a "if (nullptr)" guard around the onMarkChanged handler fixes the problem for me, and the waveform marks are all in the right places so that may be the easiest way to fix it.