I'm working on day-to-night milky way timelapses and couldn't get the mask to properly animate in one case. I followed the animation tutorial and used the "correct" method i.e no adjustments in the first mask, etc. What I ran into is when the oval mask rotates from less than 45 degrees from the horizon in one keyframe to more than 45 in the following keyframe the oval slowly transitions from an oval at one keyframe, to a circle, then back to an oval at the subsequent keyframe in the preview. Going back to the keyframes, I noticed that when I rotate the mask from less than 45 degrees to more than 45 degrees, Lightroom moves the rotation pin from the bottom side of the oval (short axis) to the lower end of the oval (long axis). I assume this is the problem.

Any thoughts how to get around this?

I really like LRTimelapse and have had good success with other similar milky way timelapses

Yes, this is a known issue when rotating over a certain degree, then Lightroom flips from +45 to -45 or vice versa.
The solution is to roate the starting mask already by 45 (or -45, you need to experiment) degrees and then use this rotate mask along the sequence - bring it subsequently to the next keyframes and adjust the rotation accordingly. Usually that way you will be able to do it.

Thanks. That's what I ended up doing in this case, but it wasn't a perfect solution since the milky way started at a low angle, and I had to also have the mask start at a low angle, then rotate both through 45 degrees. I guess I just need to plan my shooting so the milky way doesn't start at a low angle as it rotates towards a higher algle - which doesn't happen often from my location.

Hmm, normally with the technique I described, you should be able to do such movements.

On another note: If you shoot the Milky Way with a decent fast lens and the visiblity is good, you shouldn't need a radial filter at all.
Often I find sequences where people use animated circular masks on the milkyway, look artificial.
Maybe you would like to share one of your results?

I'll try it some more.
I did shoot with a fast prime 20mm lens with a Bortle 2 sky anad should look good with only very minor edits. I want to enhance one copy of the video that I'll be projecting on a screen in a fairly well lit room so am increasing the contrast using curves and a little dehaze. I'm also using the Camera Stamdard profile