debusine-server-artifacts-cleanup.service fails with a Database error

I am observing that the debusine-server-artifacts-cleanup.service fails in similar ways on two debusine deployments. The service is marked as failure by systemd as the command exists non-zero. The journal looks like this (slightly redacted):

Dec 13 00:00:11 poseidon debusine-admin[2121869]: System check identified no issues (0 silenced).
Dec 13 00:00:12 poseidon debusine-admin[2121880]: CommandError: Database error: ("Cannot delete some instances of model 'WorkRequest' because they are referenced through protected foreign keys: 'CollectionItem.created_by_workflow', 'CollectionItem.removed_by_workflow'.", {<CollectionItem: Id: ... Name: build-arm64 Parent collection id: ... Child type: b>, ...})

On another server, the "Name" is build-all and there are more references, but the symptoms are roughly the same.