Issues with members who canceled but want to resubscribe, can't!

There seems to be a problem with the register link for old members who had cancelled their membership and have a login already, but can’t re-register.

It used to work so that people could re-activate their membership, but now there are users who say they’re getting a “cannot process” error message.

What do I do in this situation and why is there no “pause membership” function?

Thanks in advance for any help and insight!