Cannot edit comments, internal server error 500

This is very likely a problem with your web host. My former host runs a Resource Manager that gets “very aggressive” whenever the workload on the server (i.e. – other customers using the same physical computer as a web server that you are) gets heavy. It would then start canceling any process that used even a moderate amount of processor time. Like your 999 comments to be displayed.

Admittedly, my problems were with phpBB Version 2, but the same would hold true for WordPress as my issue was processor-intensive MySQL queries that caused me to have hundreds of 500 errors (to myself and hundreds of site visitors).

Best way to figure it out is to file a Trouble Ticket with your web host giving exact date and time (tell them what time zone you are in, so they can translate) of a 500 error you are getting for this 999 comments thing, and ask them for all log information they can find.

And don’t delay. Finding log info after 24 hours can be a lot tougher for some web hosts than incidents that occurred the same day.

In my case, the results were quite telling, as I tracked it down to a very complex MySQL query to build the information for a feature that almost no one used!

Good luck with it!

500 errors can be very frustrating because they can be either WordPress configuration or other problems. Or they can be caused by a web host that goes around automatically cancelling legitimate Processes that you are running.