MFX_ERR_UNKNOWN is returned from SyncOperation()

Hello All,

I have implemented an encoding product with Intel Media SDK 2016 R2 and sample codes.
So I have met an encoding problem in a sample code.

[Issue 1]
It is occurred an INIFINITE loop at GetFreeSurface() in sample_utils.cpp with a relatively low frequency
which is located the loop calling at GetFreeSurfaceIndex() and MSDK_SLEEP() alternately.

In this case, I have inserted a work arround as follows;
Add a number of two allocation frames at CEncodingPipeline::AllocFrames() in pipeline_encode.cpp.

nEncSurfNum = EncRequest.NumFrameSuggested;
nEncSurfNum += 2;

And then, I met a different problem as follows;

[Issue 2]
An error MFX_ERR_UNKNOWN is returned from SyncOperation() at CEncTaskPool::SynchronizeFirstTask() in pipeline_encode.cpp.
which is occurred with low frequency same as Issue 1.

How can I resolve the problem with what fix I should make?

Best regards,

Mitsuteru Watanabe