The task "Docker - Delete unused manifests and images" is intended really for only docker hosted repositories.
When running this task for "All repositories" the task will run on all docker repos (including docker proxy repos). This task is intended for hosted repos.
For docker proxy repositories, clean up task makes more sense.
If there are many hosted docker repositories then you have to set up many individual tasks of "Docker - Delete unused manifests and images" for each docker hosted repository.
Improvement request is
1) When "All repositories" is selected for this task, then the task should only run on docker hosted repos.
2) When selecting an individual repositories, only docker hosted repositories should be selectable.