Unable to log into classic server that have characters on them

As per the title, I am unable to log into the wow classic servers in which I have active characters. I can log into other servers and create chars and play them, but if I swap servers or log out I cannot log back into that server again.
On servers where I have characters, it sits on logging into game server for a little while and then DC error WOW51900328.
I had a raid planned tonight where I’m the raidleader and main tank so pretty gutted I was left unable to play all day.
I was able to log in around midnight, some 14 hours ago, and play normally for about an hour, but from this morning I have this issue.
Tried reinstalling, purging cache, the 128ms fix in the other thread, anything. Just can’t get in on my own bloody server and play…

I am running windows 10 on a normal broadband fiber (whatever one such is called) connection. No linux or tethering or anything.