I installed your add-on for testing on a client’s forum, and the same problem is happening there.
New registrations are shown with the message Same IP, and the IP shown is the server’s IP.
The add-on was installed without any changes.
This test on a completely different server proves that the problem probably cannot be caused by my new server. The same error happens elsewhere too.
If this is caused by a wrong setting in the add-on, then that wrong setting is the default setting of the add-on.
Either way, there must be a reason why so many users are suddenly shown as if they had registered from the same IP. Whether it is a configuration problem or a bug in the code, it needs to be fixed, please.