Jumpy select2 token dropdown (on Mosaico subject editor)

Found a strange bug with select2 dropdown jumping around when you click / type.

I've found it specifically for the token selector on the subject editor of Mosaico New Mailing screen.

Here is regular Island:

Screencast from 2024-07-09 14-49-56.webm

Here is riverlea version:

Screencast from 2024-07-09 14-51-23.webm

I can't see it anywhere else (yet) so maybe something weird about the markup around that field?

I can reproduce with all different streams in v0.8, on two different sites.

Both are D10 with Claro so I guess it could be that (will try with Standalone later)

Not really sure where to start with fixing... Select2 is always a bit weird in how it sets style tag directly on the elements using JS. In this case I think it's intermittently setting very large width and negative left ...