On my danish domain Jernbanen.dk, at least 2 german users gets HTTP error 500. I´ve asked them, if they use IPv6 but no reply yet.
A dane has tried using IPv6 and gets HTTP error 500. When connecting without IPv6, the forum works as expected.
You can check your IP-version here: https://test-ipv6.com/
I connect through IPv4 and everything works on my pc.
All Akismet is turned off in all forums.