Watch star is functional to non-JS browsers on mobile and desktop.
This impacts both Vector AND Minerva so is an issue in core.
(Not able to replicate)
Visit https://en.m.wikipedia.org/w/index.php?title=Spain&action=unwatch where Spain is watched
I've definitely seen this issue before (in Vector) and it's a race condition/caching problem and not specific to Minerva. I cannot replicate this right now...