@IvanMiskalo thanks for the clue on this one. We were able to track one of these crashes down recently that related to Sequencer. It has been fixed for the next release (5.6). In case anyone is encountering this and is compiling from source, the fix is:
https://github.com/EpicGames/UnrealEngine/commit/8dae0ba8303832313b8b88ef47e4431b64b6f34e