i have about 6 of these errors with different times but the error is the same
2020-06-23 10:18:59: (mod_fastcgi.c.421) FastCGI-stderr: PHP Warning: SQLite3::query(): Unable to prepare statement: 11, database disk image is malformed in /var/www/html/admin/scripts/pi-hole/php/groups.php on line 211
It's the query history (long term database) and the network details (network overview). You adlists, black/whitelist will be preserved (stored in /etc/pihole/gravity.db)