On my current tests on meta, this almost never happens anymore wether though the collapsing repro mentioned in the link post, or your note of switching from one app to another. I know it can still happen from time to time, especially on PWA, but I can only fix some of the bugs of apple 
and PWA is clearly the worst of all, direct browsing in safari or discourse app is less buggy AFAIK.
Note that I have plans, to fully revamp how the composer is displayed on mobile, but this is longer term plan, those fixes are mostly trying to extinguish the fires created by Apple, I also hope in the next weeks they will keep fixing more bugs.