Yes, it does appear to be related to using iOS or Safari. A post I submitted yesterday morning on my iPad ended up full of question marks instead of apostrophes; I had to edit out all contractions in order to get rid of them. When I post from Chrome on a Windows computer (as now) all characters appear correctly.

That said, some of my older posts have changed to contain question marks as well, notably my tutorial thread on making a wiring harness. I may have drafted those posts on my iPad but I'm sure they passed through my desktop before being posted since they contain so many images. The text in those posts appeared correctly when posted and only became corrupted recently.