[bitfolk] Apache handing on Ubuntu 16.04

Hi all, Sorry if this doesn't belong here, I'm having a bizarre problem with Apache (2.4.18) on an ubuntu 16.04.5 bitfolk VPS, just wondering if anyone might be able to shed any light as I'm at a complete loss. Any pointers would be much appreciated. Over the past week or so my Apache installation has an issue where it just.. stops responding and requests just time out until the server is restarted, 12 hours later same thing happens, lather rinse repeat. Top / Htop show the expected number of apache processes / threads running (<10) but clearly they aren't doing anything, memory is 60% utilised, < 0.1 load avg, 30% disk usage. I'm using apache2 + mod-php7 (not ideal, but it's something I plan to change later) just for a few low traffic Wordpress sites. Using sane prefork settings for a low(ish) memory VPS. Nothing obvious in the apache logs other than they just seem to go silent reflecting the dead server, entries resume again after restarting the server. dmesg has no hints either. Thought it might be a DOS / brute force scan attack and maybe apache child processes are hanging for some reason and not being terminated after maxRequestsPerChild, or the server is saturated and not responding because of a backlog but there is no load.. After apache2 restart everything works perfectly again just for a while. Not sure how else to diagnose the issue :( Cheers, Luke T