Pop-Up "New Backup Server" does not have any effect

I recently did an reinstall of the OS of my UrBackup Server, reinstalled UrBackup and restored the configuration.
Two Windows 10 UrBackup clients resumed backing up without problems.
On the third Windows 10 UrBackup client, a pop-up was diplayed, asking if the new backup server should be used. Despite clicking on yes, the new server is not used and the server displays “Server rejected” for that client on the status page.
Adding the server identity manually to the server_idents.txt on the client helped.

Note: Is it expected that the server_idents.txt is only accessible for admins?

Client Version: 2.2.6
Server Version: 2.4.11