My Pi-Hole is now up for a little over 2 weeks.
In those two weeks I restarted the DNS server twice because blocking seemed to have stopped.
It could also be that logging only stopped, but I haven't checked this.
The reason I noticed, is because suddenly it would say that no DNS queries were made all day in the dashboard.
Does this sound familiar to someone, and is there a good way to solve this?
Nope:
$ uptime
00:57:07 up 47 days, 6:55, 2 users, load average: 0.02, 0.01, 0.00
$ pihole -v
::: Pi-hole version is v2.13.2 (Latest version is v2.13.2)
::: Web-Admin version is v2.5.2 (Latest version is v2.5.2)
You could check whats happening in the Pi-Hole logs:
less /var/log/pihole.log
Or the syslogs:
less /var/log/syslog
Or check the kernel ring buffer:
sudo dmesg | less
And you might be asked to create a debug token and post the token here "Debugging With A Medical Tricorder":
https://pi-hole.net/2017/02/10/how-to-contact-the-pi-hole-development-team-for-support/
We are all here and can help you 
Please so some digging using the commands @deHakkelaar suggested.