I faced the issue a few times during the update to Checkmk 2.0
I will share tomorrow my notes to solve the problem.
If I remember correct: This happens e.g if you activate the management board for a host and didn’t configure anyone. This will mostly happen, if you enable this on a folder base with hosts in there with no Management board. In this case you need to modify the hosts.mk to solve the problem. I will share tomorrow my notes.
BR
Anastasios