After long time, I opened again the BOINCSTATS and noticed that my Einstein contributions are missing completely. There simply is not Einstein entry in the list of projects I am working on.
How come?

Try GDPR

John, thanks for the hint. After having read on the site mentioned by you, I went back to the Einstein site and found out that on my preferences, under "privacy" the box about allowing them to export my data to BOINC was not checked. So I corrected this.
Guess it might take a little while (a few days?) until the Einstein data shows up in my BOINC stats, right?

For sites listed at the given GDPR link, their policy obviously limits the stats at boincstats.com . If I go to a project's "server status" page at their own website, I see many more users than what are listed here at BOINCstats. For example, compare the following...

1. https://einsteinathome.org/server_status.php
   
2. https://www.boincstats.com/stats/5/project/detail/
   

My question is, are the *project* stats limited? That is, is the following (at 2nd link above) correct?
Total credit: 453,315,954,708

Oh, I answered my own question
https://einsteinathome.org/content/which-stats-are-limited-when-users-dont-share-stats