While I can confirm updating to latest release containing the mentioned fix
Core version is v6.4 (Latest: v6.4)
Web version is v6.4.1 (Latest: v6.4.1)
FTL version is v6.5 (Latest: v6.5)
the query log at https://pi.hole/admin/queries finally loads lightning fast (instant) again, I'm not sure about (will need to monitor this for a while) the
But that is another topic. The original issue of this issue is solved now. Thanks.