Hey Igor,
Thanks for your patience, and thank you for raising this. I’ve logged a bug that you can follow along with,
https://issues.unrealengine.com/issue/UE-265587, it can take 24 hours or so for the bug to show up in the issue tracker.
The primary issue is that the conditions get hard referenced and tracked in the MovieSceneCompiledDataManager.hierarchy stack for other reasons; when you destroy the level sequence actor, the conditions inside will cause a crash.
You can try making FMovieSceneSubSequenceData.Condition a TWeakObjectPtr, and then fix up FSequenceUpdater_Hierarchical::Update’s reference to it to address the bug.
Unfortunately, though I don’t have any other options to address the bug.