So my wordpress site keeps going down from a 500 error, about once a day now.
The entire site, including the wp-admin, will go down and stop responding to all requests with a 500 error.
If I enable WP_Debug I only get a warning: Warning: Illegal offset type in ...../wp-includes/cron.php on line 99
The warning is the ONLY thing that appears on the site when WP_Debug is enabled, nothing else. All requests are blank except for that warning.
When I check my server logs I can see that just before the 500 error started happening a PHP script ran out of memory: PHP Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 560537 bytes) in .../wp-includes/functions.php on line 434
All out of memory errors happen on the same PHP file at the same line. I know what you're going to say, "Bump up the memory in your php.ini". Well, it's already 128MB so I'm not sure that's the right answer. This configuration ran fine for months, this just started happening a few days ago.
Restarting Apache2 temporarily resolve the problem, until the next day.
The server this is happening on is shared with several dozen other wordpress sites, they are all unaffected by the problem this site is experiencing.
I'm tearing my hair out over here. There's a 500 server error happening and there's ZERO logging/reporting to tell me what's causing it, then it magically disappears for 24 hours if I restart Apache.