Anything stored in the dbase ?
echo 'SELECT count(*) FROM queries WHERE timestamp BETWEEN "'$(date --date="2020-09-4 00:00:00" +%s)'" AND "'$(date --date="2020-09-5 23:59:59" +%s)'";' | sqlite3 /etc/pihole/pihole-FTL.db
Whats output for below ?
stat /etc/pihole/*.db
I have no clue yet whats causing this.
Is any other software installed on this Pi ?
Did yo make any alterations on top of the default Raspbian Buster install + Pi-hole ?
You could try default a bunch thats related to the web GUI.
Figure out currently installed PHP packages with below:
apt list --installed '*php*'
Purge/uninstall them all including the lighttpd package with below:
sudo apt purge lighttpd <PACKAGE_1> <PACKAGE_2> <PACKAGE_3> etc
And select repair with below one to have them all installed and configured fresh again:
pihole -r