So,
I've been testing pihole for some time now and it worked just fine until it stopped working altogether. First it stopped resolving DNS and then i was not able to login.
Long story short it turned out that logs consumed all my space (since i was lazy enough not to install nagios on this VM)
So just a suggestion that you add some kind of warning when all space is consumed.
I ended up resizing parition and deleting logs (so far it's working flawlessly).