After the last update of pihole v3.2.1, web interface v3.2.1 and FTL vDev ((no, v2.13 ), only the query chart is available at the pihole console page.
The rest is not visible or is loading.
Restarting the Raspberry does not change anything.
after updating to the latest software version I experienced the same issue.
When opening the pi-hole page after several time and a succesful log-in, the charts are empty. F5 or refresh will help to get the page working.
But this is a different behaviour to the former sw version.
This behaviour can be repeated many times a day, when I have to log in!
I had this problem upon updating two Pi-Holes and found that clearing the browser cache fixed the display issue. I even wiped an SD card and started over and still wouldn't load until I cleared the cache.