Would be great to have when trying to align camera & actor.

Thanks for feedback. I understand general need for undo/redo, and we plan it for future versions. However, it is not clear why it is needed particularly in the context of aligning of camera and actor.

Is your suggestion about single-camera or multi-camera mode?

Single camera. Analyzing the actor appearance can give unexpected results, the actor being repositioned and also the background. Don't know if I missed something reading through the instructions, but I figured ctrl-z would quicker give me a new chance to sort things out.

The "Analyze actor appearance" button moves the camera, not the background. I guess a "Reset camera" button should help in your case. That's easy to do, maybe we will add it in new version.

Usually "Analyze actor appearance" button should not create any problems. If it does, then probably your input video is not completely ok. Please make sure that your video is shot properly:

Actor is dressed in compatible closes (solid-color long-sleeve shirt or T-shirt over long-sleeve shirt).
Background is not very cluttered.
First few seconds of the video contain only background.
Actor is in T-pose when you click "Analyze actor appearance".
Camera is panned/tilted to roughly align model with actor image.

You got it, finally, in v2.2.0.144.