From Primegrid:
It has come to my attention that Nvidia recently released a new video driver that is causing widespread problems. 397.31 seems to cause the GPU to become inaccessible to both CUDA and OpenCL programs after a while, and can only be reset by rebooting the computer. It's likely this affects all BOINC projects and not just PrimeGrid. Indeed, it probably affects all GPU programs, even those that don't run under BOINC. There's a newer, hotfix driver 397.55 which seems to correct the problem. I strongly recommend either upgrading to 397.55 or rolling back to a driver earlier than 397.31.

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They seem to be having one problem after another with their drivers lately.

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Though I did not experience any problems with the 397.31 driver, I've updated to 397.55 as a precaution.
The NVidia download page still offers the 397.31, so this can't be a widespread issue.
However, you can download the 397.55 from here.

Seti, Einstein also have issues with this new Nvidia update.

Most driver updates are related to games and not computational updates so it is better to wait before updating unless there is demonstrated benefits to doing so.

This is an example of why being the first isn't always to best decision.

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The v397.64 WHQL driver has been released, you can get it from NVidia directly.