Marking this one as a tracker for https://issues.redhat.com/browse/ACM-5200 (Document the use case where tolerations need to be added to Placement object when using ApplicationSets).
It turned out that a certain toleration was missing, so the ACM documentation (2.7 and newer) should be updated accordingly.
If the toleration has been added, everything works fine, see comment #20.
Removing needinfo as it's no longer needed.