Mystery solved!
putting a matching note in my login notes that says "don't worry about it"

Cheers

why are there two seemingly identical sites hosting the same content but with slightly different URLs?

https://forum.puredata.info/
https://forum.pdpatchrepo.info/

I get confused every time I go look up my auth stuff for this forum, because I have an account registered for forum.pdpatchrepo.info, but not its identical (evil?) twin forum.puredata.info.