Nostalrius Begins - Quality wow vanilla realm (1.12)

When i am getting invited to a guild, the 'x has invited you to 'guild name here' pops up. When I hit accept, it doesn't work. I've tried relogging, reloading ui, etc. When they try to invite again, nothing happens. The guild is not full, as it has 341 members.

The cap has been 321. If it changed, I'm gonna assume the new cap is 341.