The reason that all of the credits are gone and you need to reregister is a new law that recently went into effect. Your account was dormant for nearly 10 and the new law mandates that after a certain amount of time all personal info, such as accounts, user names and passwords have to be erased from the servers. Your user account was beyond the deadline so it and presumably the credits that went with it have been erased. I don’t know if it is possible get them back.
The scientific work that you did for the project is still safely stored and available to the climate scientists.

Deadline on Boinc project? It must be joke.
https://boincstats.com/en/stats/-1/user/detail/914/projectList
I have all credits from retired projects. So why active project remove accounts, credits? I will never participate in this project again without credits back. It is better to crunch Bitcoin.

From Andy at CPDN staff:

To comply with the Data Protection Act 1998, we are required to only keep personal data for as long as it is absolutely necessary. We will therefore only keep records of inactive volunteers for three years from now on. Initially any records inactive since 2014 or before that date will be removed. We will continue to remove records that have been inactive for three years or more on an ongoing basis.
Therefore anyone who signed up prior to this and has been inactive for over three years but wishes to renew their engagement will need to set up a new account. If you have been inactive for the last couple of years and wish us to retain your email and username, please reactivate your account as soon as possible.

Project credits from these accounts will be retained but will no longer be linked to an email address or username.

Current, active, volunteers, or those who have been active in the last three years, will not be affected by this policy.

An Update.
After posting, I tried changing the "Community preferences" from "In a single daily email" to "Immediately, by email", and I just received a notification from this thread. So it works if using "Immediately, by email".

I'm going to switch back to "In a single daily email", and see what happens.

Perhaps worth putting it in the announcements for those who monitor that thread. I know most of those will spot this but there may be a few........

Yes, they are the test batch. (There are actually 3 separate test batches.)

If you see anything odd happen to one of them, please post about it.
Even things like the percentage progress being way out compared to the amount of time run, or the zips gradually increasing in size as it progresses, etc.