For docker see:
Are you also using the docker image? If so, see the link above.
Pi-hole Version v3.3 Web Interface Version v3.3 FTL Version v3.0
Seems (fingers crossed) to be running well.
Even pihole -t seems more responsive.
I just had this occur to me. Tracked it down finally to timestamp issues on reboot. When my singleboard computer reboots, its clock is set to some time in the future. If some requests come in while it is in this state, pihole treats that far future date as "today". When ntp finally gets around to updating the time, all incoming requests are now too far in the "past" to be considered valid. Restarting pihole does not correct the issue because it reparses the entries in the log file. You must delete /var/log/pihole.log after the time is set correctly, and optionally remove any future entries from the queries table in the db file.
I've updated my startup scripts to require pihole and dnsmasq to start up after ntp, but I have not yet restarted to verify that the time is set correctly before dnsmasq starts logging entries.