Page underneath the overlay flashes for 1 frame when switching between loading overlay and real overlay. This seems to be a problem with overlays in MobileFrontend and Minerva that use loadingOverlay: categories
The video below demonstrates the issue with the following overlays: editor (wikitext) and talk (previously fixed). The same was applying for categories.
(Recorded on https://en.m.wikipedia.org/wiki/The_Fighting_Temeraire using Chrome on desktop, but the same can be seen on real mobile devices.)