We received an update from Acronis, regarding the backups which were not started for some customers between 23rd - 27th May 2021:
The R&D Team confirmed this was caused by the recent issue related to the Data Center incident I suspected.
The incident resulted in some protection plan policies to get revoked from the agents though not displayed as such in the Protection Console.
A general solution to avoid this happening in the future will be applied with the C21.06 release.