Hello,
I'm not sure how I should title this but I think that a support member can fix this.
Here in #demo-threads you are able to create a ticket which opens as a 'private thread', but when you "leave" this you can not access it again, but it will keep the thread open.
This means you have an active ticket - in a thread - which you can not access. If there is a limit, you are not able to create a new ticket.
If you leave a private thread (ticket) it should automatic close, since the OP left?
Small update: I am not able to create any ticket in the server now.