Going strictly by that message alone, your Pi-hole wasn't aware of any upstream DNS server to forward a query to at that time.
Did you perhaps test or switch to different upstream DNS servers for your Pi-hole at that time?
If that's not the case:
That observation - along with REFUSED log entries - would suggest that a client has exceeded Pi-hole's rate limit.
If a client would be expected to exceed the default 1,000 queries per minute, you may adjust that rate limit via pihole-FTL.conf.
This would often be the case if a router had been configured to use Pi-hole as its upstream DNS server (as opposed to distributing it as local DNS server via DHCP). A debug log shows only a fraction of Pi-hole's log, but almost all contained queries originate from a .70 address.
Would that be a router?
However, you should then also see a corresponding RATE_LIMIT message in Pi-hole's diagnosis view - and your debug log doesn't include such a message. 
Yet your debug log shows some database related errors about missing tables in Pi-hole's gravity database.
This may be a bit of a far call (as the error messages involved do not match), but since you are dealing with a fresh install, you may unintentionally have corrupted your database by running pihole -g -r - see Error: no such table: main.gravity - Pi-hole v. 5.6 - #2 by DL6ER.
And likely unrelated to your problem, note that your other DHCP server distributes another .14 IP address besides your Pi-hole's .26.