I can confirm this bug.
I just ran into the same problem. Spent a couple of hours implementing availability and service periods in CRE. But service periods were just ignored in the availability reports as if they weren’t defined. Double checked with the documentation to make sure that this feature is not restricted to CEE. Spent even more time debugging.
As a last resort, I remembered the forum.
And indeed, this bug has been reported nearly three years ago. Not only once, but twice in 2020. Both threads were closed due to inactivity.
Something is rotten in the state of Checkmk…