That is weird.
I'm not sure what's going on, i tested it in Edge and after saving and viewing it again, it seemed fine. Tho I use Windows 10, so it might be a Win 11 issue. But maybe it has to something to do from your side? like a file save issue or something? I'm just as confused as you are.
for the IOS one however, I think that's the case of the program just not supporting form fillable pdfs. it also doesn't in my android phone. Maybe there's an adobe acrobat app for IOS that lets you edit them?