This is a remaining case of [Link Removed]. If you drag and drop an empty actor from Modes panel to Sequencer, the actor's transform track can't be edited.
1. Create a new level sequence
2. from Modes panel, drag an empty actor and drop it to sequencer
3. The actor is now added as a spawnable, but Transform tracks for the actor show 0.0 and can't be edited
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-51678 in the post.