I have a Ubuntu Linux X86-64 GTX950 systems... that until recently was working well processing SETI... Now, BOINC will load up a batch of GPU work and then continually keep swapping out GPU tasks not letting any of them run, it swaps the a task in and then a second later swaps it out for another task. Right now it has about 20 tasks (0.228 CPUs + 1 NVIDIA GPU) postponed, and it keeps swapping themn in and out. The GPU is not getting any utilization.

Help???

I'd check the errors you're producing: https://setiathome.berkeley.edu/results.php?hostid=8234342&offset=0&show_names=0&state=6&appid=

<core_client_version>7.8.3</core_client_version>
<![CDATA[
<message>
too many boinc_temporary_exit()s</message>
<stderr_txt>
WARNING: boinc_get_opencl_ids failed with code -1
Error: Getting Platforms. (clGetPlatformsIDs)
BOINC assigns slot on device #0.
WARNING: BOINC failed to provide OpenCL device, using own enumeration abilities
ERROR: OpenCL kernel/call 'clGetDeviceIDs (second call)' call failed (-32) in file ../../src/GPU_lock.cpp near line 1311.
Waiting 30 sec before restart...
WARNING: boinc_get_opencl_ids failed with code -1
Error: Getting Platforms. (clGetPlatformsIDs)
BOINC assigns slot on device #0.
WARNING: BOINC failed to provide OpenCL device, using own enumeration abilities
ERROR: OpenCL kernel/call 'clGetDeviceIDs (second call)' call failed (-32) in file ../../src/GPU_lock.cpp near line 1311.
Waiting 30 sec before restart...

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OK, what do I do about this?

Post the first 30-40 lines of your BOINC start up messages.
And if you haven't yet, tell which videocard drivers you use and where you got the from.

But I suspect from the error message that your GPU is only recognized as a CUDA device, not OpenCL.
Or the wrong OpenCL.

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Just a heads up...

I recently got these errors (pasted below), including "postponed" message for GPU tasks, on a Windows 10 v1803 PC, that has 3 GPUs: GTX 970, GTX 660 Ti, GTX 660 Ti, with NVIDIA 397.31 drivers.

When I restarted BOINC, it did not see the GPUs at all (CUDA nor OpenCL!)
Also, the NVIDIA system tray icon said "update available", and GeForce Experience said "Driver not found".
When I restarted the PC, everything was fine again, including BOINC GPU detection, and tasks running successfully.

From my experience, and additional research that I've done, I believe:
The NVIDIA 397.31 drivers have a problem "staying installed/detected" on Windows, and NVIDIA is working on it. Restart the PC as a workaround.

PS: Yes I recognize the original poster has Linux. So the issue may not be exactly the same.

Running on device number: 0
Priority of worker thread raised successfully
Priority of process adjusted successfully, below normal priority class used
WARNING: boinc_get_opencl_ids failed with code -1
Error: Getting Platforms. (clGetPlatformsIDs)
BOINC assigns device 0
WARNING: BOINC failed to provide OpenCL device, using own enumeration abilities
ERROR: OpenCL kernel/call 'clGetDeviceIDs (second call)' call failed (-32) in file ..\..\..\src\GPU_lock.cpp near line 1310.
Waiting 30 sec before restart...