To resolve the issue, do the following:

Create a new Active Directory group that is named „ContentSubmitters“ and then grant Admistrators and NetworkService full access to the group. This is a dummy group and should be used as a placeholder only. You might want to add a description so that the group is not removed.

Force or wait for Active Directory replication.

Restart the following services:

Microsoft Exchange Search

Microsoft Exchange Search Host Controller

via Content Index status of all or most of the mailbox databases in the environment shows „Failed“.