This happened to me recently and I couldn't find any related posts through a quick search. Figuring it may happen to other people, I've decided to write one myself. I'll try to be as brief and to the point as possible.

It happened using grcpool, but I'm guessing that depending on your configuration it can happen without using grcpool.

Preconditions

Have at least 1 CPU project with the same priority (Resource Share) as Einstein. In my case, VGTU with Resource Share 100

Have at least 1 GPU project (in my case Asteroids) in addition to Einstein, with whichever priority.

The problem

Einstein task (using GPU + 1 CPU) finishes Different GPU project takes the GPU but no CPU CPU project takes free CPU When Einstein wants to work again, all CPUs are taken. Depending on the CPU tasks deadlines, it gets denied CPU usage because meeting the deadlines takes priority. This locks Einstein out of running its GPU tasks.

The fix

(Maybe not all of this steps are required, but this is how I fixed it)

Change Resource Share of CPU projects to be lower than Einstein (in my case Einstein has 100, VGTU 50)

Resynchronize client (if using grcpool or some other manager)

Suspend any other GPU project running (Asteroids for me)

(Optional if still not working) Suspend the CPU task with the latest deadline.

After applying the fix you can resume the suspended GPU project, I have yet to check if the next time Asteroids runs it locks Einstein out of the GPU again, or if everything runs smoothly with this new configuration.

Sorry if this is common knowledge or if there's already some post explaining this. I'm pretty new to BOINC and gridcoin, and since it happened to me because I configured a GPU backup project when I read the announcement that Einstein was going to have downtime on the 23rd for hardware improvements, I figured more people may be in my same situation.

Happy mining :)

Edit/Update:

My proposed fix seems to work but there's still something funky going on with the priorities. I have now my Resource Share set as Einstein (GPU) 80 / VGTU (CPU) 10 / Asteroids (GPU) 10; with Einstein also using 1 CPU as I said, and Asteroids using no CPUs; but I'm seing Asteroids come up a lot more than what my configuration would suggest.

From what I could find out reading on forums and whatnot, apparently BOINC has some internal "high priority" mode that sometimes activates for CPU tasks depending on deadline, so maybe that's playing a part. I may do another post in a few days with more data and/or findings.