I have a dual xeon system that was idle and with cooler weather I fired it up and allowed CPU tasks. It has three RX560 also.

I got a lot of ATI separation, 146, not problem, but instead of n-body I got way too many single thread separation. I went to preferences and put an [X] in the n-body and remove the [x] in the separation. I suspect that will also stop the ATI GPU tasks. Poking around I see that the single thread has been depreciated so I was wondering if that applied to the Linux apps or just the windows. I am running 18.04 ubuntu. I also aborted the CPU tasks (sorry) as I only wanted to run a few n-body to see how they preform. I will try to set up a limit on download as all I wanted was one cpu task. Not sure how to do that and still allow the RX560 to work.

[edit]
Got an n-body.
used <project_max_concurrent>4</project_max_concurrent>
and am running three RX560 that take 3 minutes each and one 16 core cpu bound tasks that looks like 11 hours to go. The "11 hours left" is decreasing by 8 seconds for every two seconds that elapse which is good sign. Not sure if I will get any more gpu separation runs but won't know till the 260 WUs left have finished.

OK, finished one MT task and got 100 more downloaded. Unfortunately, The ATI GPU queue ran dry as I need to exclude single thread tasks which also stopped the GPU ones.. I will stop all cpu tasks. Hopefully boinc will not terminate the ones in the queue as I don't mind letting them finish

run time	cpu time     	credit
1,662.06	18,551.19	159.62  Milkyway@home N-Body Simulation v1.76
215.03		7.55		227.51	Milkyway@home Separation v1.46 OpenCL RX560

So 28 minutes -vs- 3.6 minutes

If any staff is reading this please add my wish: change the project preferences from "separation" to be "gpu separation" and "cpu separation". If the separation work units are the same for gpu or cpu then maybe there is an app_config directive to tell the gpu to process the single thread tasks. That is just a guess.