This link has the solution. You have to delete the control rig that comes with the character when you add it into a new sequence, then add your own animation in after that.
Weirdly my blueprint was also misbehaving and staying standing up after, but it works in the sequence, so that’s all that matters. buggy though. Here is the link with clearer screen shot. Skeletal Mesh Mannequin Not Animating in UE5 Sequencer? - #2 by Quetzalcodename