Hello Marcos,
thank you for your reply. My fault, thank you for opening my eyes
Meanwhile, I got a response from one of our affected users.
Because of this feedback, I think, I can say, that ESET is not the cause for this behavior. The cause seems to be the update from MacOS 11 to MacOS 12. Something seems to went wrong while the update was running.
Our employee told me, that he had to log in with his Apple-ID after every new boot of his Mac. While the login process, he was able to see, that the keychain was changed. It seems, that he got a new keychain at every logon with his Apple-ID.
He did a reset of his Mac and a fresh installation with MacOS 12 and after that, he installed ESET EES (Version 6.11.1.0) via our software deployment Jamf. Since that time, his keychain stayed unchanged.
In summary, you can say, the case is solved.