The checks were using an uncommon service description for their checks:
Notification Spooler [site] ...
Because those processes are logically tied to the OMD sites, it makes more sense to make them match the other OMD site check naming scheme:
OMD [site] Notification Spooler
This has now been changed. It will automatically be applied to new sites. Existing sites will only use this new description after enabling it via Global Settings and performing a rediscovery of the services on the affected hosts.