Please upload a debug log and post just the token URL that is generated after the log is uploaded by running the following command from the Pi-hole host terminal:
The client IP shown in your above screenshots falls into the 172.16.0.0/12, which often suggests a Docker environment (though Docker's default bridge network usually would start with the more specific 172.17.0.0/16 subnet range).
If you were running your Pi-hole in a Docker container, gravity won't be accessible until shortly after container startup.
Similar may be true for a brief period during gravity updates when database is switched from the previous to the updated one.
If gravity is inaccessible, Pi-hole won't be able to determine whether a given domain request should be blocked.
Pi-hole's default behaviour is to allow all DNS requests during that brief period. (click for more)
It would depend on your chosen platform and configuration how brief "brief" actually would be.
In a Docker environment on an RPi Zero with a huge gravity database alongside other software like home automation and a media server, switching databases will certainly be slower than on the same Zero dedicated to a bare-metal Pi-hole installation with just the default blocklists exclusively.
That said, a bare-metal Zero is an adequate platform to run Pi-hole in a home network. I've been using that configuration (with a 400k to 500k strong gravity db) for years now, without ever producing any observations like yours - but maybe I was just luckky enough that my network never was busy during gravity updates.
This behaviour can be changed by adding and adjusting the value for REPLY_WHEN_BUSY in pihole-FTL.conf (In case you run a dockered Pi-hole, make sure you have the proper volumes in place.).
Note that by using any other value than the default ALLOW, you will effectively cut your network from DNS resolution until gravity is accessible again.
Response to your answer-post:
Since I can't find a solution, no data at all displayed by Pihole, I set the debug function:
[?] ** FINISHED DEBUGGING! **
The debug log can be uploaded to tricorder.pi-hole.net for sharing with developers only.
[?] Would you like to upload the log? [y/N] y
* Using curl for transmission.