Login problem's fixed! As always, LMK if you're still seeing issues (here or in PM is fine).
Belatedly, regarding this thing:
...I didn't get notifications about 2 private messages from 10 April, and I saw them only today when decided to check the Forum. They weren't in Spam folder.
So, is there any chance to check and fix it?
...Both the forum and the first mail server are in Bluehost/Unifiedlayer's address space, so that looks OK, but I have to say that I'm a bit puzzled about the envelope sender ("From_") being 'pogopros@fast27.fastdomain.com' (while the "From:" header is '"The Stand Still, Stay Silent Fan-Forum" <webmaster@ssssforum.com>') ...
The fastdomain.com thing is the way that the webhost (which is technically Fastdomain rather than Bluehost--same company, same servers, but less crowded and a little more stable) handles PHP email. I believe there was a way to disguise that which we had going before the most recent migration, but there was trouble getting it to work post-migration, so this (which at least gets the email sent out properly) was the compromise. It's functional, but not pretty. If the weird sender address bugs people I can take another look.
About the main issue though, if it was just those two emails then it's likely to remain a mystery, for better or for worse. Unfortunately sometimes emails do just disappear, and there's so many factors that it can be hard to track down. If it's ongoing though, we definitely need to take a closer look.