So it looks like Hazel took a rest.
1. Preview: "Rules Matched" - but nothing happened.
So I had a look at the Console/ Hazel log: no entry there for the time in question (14:32).
2. Last log entry was at 2023-07-22 13:56:14.866 (H. did some other processing)
3. I dropped my testfile into the folder at 14:32,
so Hazel was on its 'unauthorized' rest already 36 min.
In the top menu it said "Hazel is running," but Hazel was not running at all.
So now I know that having an eye on the log will be profitable.