Step to reproduce.
You can use the default third person project to reproduce this freeze bug.
- Create a Level Sequence
- Add any mannequin skeletal mesh to the sequence, remove the control rig (cr_Mannequin_Body) so that you can play any animation
- Copy any of the animation sequence asset that can be played with the skeletal mesh in the project to create a new animation asset.
- Open the animation sequence asset in step 3, add any curve to the animation.
- click the curve and open the curve editor, and right click the curve to add a key.
- Save the animation asset
- Add the saved animation asset to the skeletal mesh in the Level sequence.
- Play the level sequence and pause so that it is paused in the middle of the added animation.
- Open the animation sequence and click the curve you added to open the the curve editor
- Drag the key of the curve using mouse.
- The engine freezes
If you rewind back the LS, and pefrorm step 8 to 10, the engine does not freeze.
Engine gets freezed if you drag a curve key of an animation sequence that is being played on a Level Sequence editor.
This is probably a deadlock caused by worker thread and main thread competing the lock on the animation.
It seems to have existed at least from 5.7.2.