I’ve had this and a number of similar issues. I’m a relatively newbie to Unreal. However, I have lost character/prop animation before and found it strangely embeded in the camera track. So I ended up continuing with adding more animation.
Perhaps I’m doing this wrong but to animate anything, I drag it from the outline onto the sequencer thus creating a new track for me to start keyframing transform properties etc. Last night, my sequencer ended up with about 15 cameras for 15 shots and about 10 different character with basic transform animation + mocap. Everytime I restarted the programe I got an error saying the sequencer didn’t resolve properly on shutdown. I hit resolve and it works fine. Unfortunately, just as I was finishing up, Unreal crashed. I can still access the project but If I open up the Sequencer to see my animation, Unreal crashed. Unreal doesn’t seem to even recognise the autosave files. So, just how buggy is the Sequencer?