Since updating to iOS 11, when I type an apostrophe here from my phone it shows up as random junk:
Seem fine when composing, transformed when previewed or posted. iPhone 6 Plus, iOS 11, Safari.
Earlier today, I was looking at some very old posts on the forum and saw these extraneous characters. I had no idea whether they had just shown up recently or had appeared in the posts several years ago. For a moment I was on the verge of trying to edit/correct some of the squirreliness in my own old posts, but I guess I could not have succeeded. Maybe things in those posts will go back to normal whenever the whatever-is-screwed-up is corrected.
BTW, my old posts weren't created with an iPhone or with anything using iOS, so I am skeptical those are the source of the problem. On the other hand, the apostrophe in the first sentence of this paragraph looks OK, so it can't just be the current setup of the forum.