I got this reply from Discord:
Hey Rune,
Sorry about the invite troubles! There can be 3 possibilities of a link being expired:
- The link itself is expired
- The IP is in the bans list for the server
OR
- The user is already a member of 100 servers
If you can contact the server admins, could you ask them to revoke all the bans in their server settings > bans menu even if the Discord Tag isn't on the list? (This can happen accidentally for any number of reasons.) If that still fails, share the link with me and I'll be able to tell you exactly which of the first two options it is.
I'm not a member of anything like 100 servers, more like 10.