So a few members of our support team have noticed a large number of 500 errors cropping up in the 2.8.x branch as of late. Normally this ends up being a plugin conflict — but we've spotted that resetting the theme to "default" or "classic" in the database, checking the site and changing the theme back brings the installs back up for most folks.
One of our admins checked on one of these sites before we found a fix. Upon running an strace, he found that the process for the site was hanging on a MySQL read or read(3.
This showed that the process was connecting successfully to the database, but was waiting for some information to be read. As that wasn't happening in time, the site would time out and spit back the 500 error.
If anyone can give some insight on why this might be happening, it'd be greatly appreciated. I'll turn over whatever information that I can to try to help solve this matter for our customers.