Project Priorities don't seem to work correctly

[Uroc327]

I was wondering why GPUGRID.net with a total allocation score of roughly 4 to 6 (almost always highest allocation score for my machine) runs only very rarely.

I was looking into boincs event log an saw the following lines a couple of times in it:

Mon 10 Feb 2020 12:19:05 PM CET | GPUGRID | Sending scheduler request: Requested by project.
Mon 10 Feb 2020 12:19:05 PM CET | GPUGRID | Not requesting tasks: don't need (CPU: job cache full; NVIDIA GPU: not highest priority project; AMD/ATI GPU: not highest priority project)
Mon 10 Feb 2020 12:19:07 PM CET | GPUGRID | Scheduler request completed

Why is my nvidia gpu often idling, when apparently there would be wu from gpugrid to work on?

Also, when boinc wants to fetch new cpu tasks, it pretty much never fetches from gpugrid either. And then if it asks gpugrid for new tasks, it sees that the cpu queue is full. This happens despite gpugrid being the project which, according to the 'how projects are chosen for this machine' site, is chosen for cpu and the nvidia gpu.