I spent days searching why my server is hanging and finally found that it almost always hangs on gc_collect_cycles() call! It's surely because one of the tricky plugin, but how can it be that such function hangs!?! Could it be a PHP bug? I'm on PHP 7.2.3. Anyway, I just would like to share this discovery For now I'm simply commented out all gc_collect_cycles() calls and hope that server survives, considering that server automatically restarted every two hours