Sounds good, thanks!
Actually, this reminded me of a similar problem that I had in the past with a different <w> effect, and I just noticed that I'm still getting this problem in build (not in editor). The problem occurs the first time the menu is shown, but it gets fixed if I close the menu and reopen it, so it probably has something to do with Rebuild().
This other one would be easier to reproduce, so I can try and copy some prefabs over to a demo project later. But either way, it looks like there's something that can situationally cause an animation to stop, which (as far as I know) isn't intended.