I've been having the same issue and am now waiting to see if purging php5-apcu helps.
When apache stops responding, it has maxed out on threads and I get this message in error.log:
[mpm_prefork:error] [pid 7628] AH00161: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting
I also have seen a apc related error:
PHP Warning: apc_store(): GC cache entry 'oc558dd98d33/AutoloaderOC_User_Interface' was on gc-list for 3602 seconds in /var/www/owncloud/lib/private/memcache/apc.php on line 21
Killing a few threads allowed me to get to /server-status on the server which showed the threads were all in "Sending Reply" states responding to owncloud/status.php requests.
I've been having the same issue and am now waiting to see if purging php5-apcu helps.
When apache stops responding, it has maxed out on threads and I get this message in error.log:
[mpm_prefork:error] [pid 7628] AH00161: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting
I also have seen a apc related error: AutoloaderOC_ User_Interface' was on gc-list for 3602 seconds in /var/www/ owncloud/ lib/private/ memcache/ apc.php on line 21
PHP Warning: apc_store(): GC cache entry 'oc558dd98d33/
Killing a few threads allowed me to get to /server-status on the server which showed the threads were all in "Sending Reply" states responding to owncloud/status.php requests.