Office 365 Licenses fail after sync

Since the maintenance contract for some Hyper-V host licenses was about to expire, I needed to sync the license information to get rid of the nagging mails. This worked so far, but in the same moment all 38 Microsoft 365 mailboxes went into unlicensed status and there is no functional way to reassign the licenses.

Installed build is 27009.

Error shown for each mailbox: The device has no license to apply a protection plan

Trying to assign licenses from Settings/Licenses - Assign - select mailboxes - Done does exactly nothing. If I try to assign the license from device properties, there is no license listed, only key or purchase options.

Support recognized the issue, but is rather slow to resolve it. (Last time this happened on customers it took about 3 month for a working build). (Case 05002627.)

Best greetings from Germany
Olaf