OMG, I think I’m starting to get paranoid
This time the problem was me.
After I had integrated the Ikea lamps, I had reactivated a Z2M device and Z2M then wanted to reboot.
This caused the message, which is completely logical because Z2M was really not there for a short time due to the reboot.
When I checked the status history of the Z2M devices again, no new “not available” entries were found.
So it seems that everything is working as it should and I have only tripped myself up.