I'm still struggling with this. When I was developing the plug-in for CPU only, I had a similar issue before I added the coded to check-out each of the layer parameters I was using. Does the GetFrameDependencies stage replace this step? I can't think of a sensible place to put the parameter check-out code in the GPU verison.
Update from me. I have now started to get some meaningful data. It appears that the GPU approach of GetFrameDependencies does not return a frame when the track is not visible, unlike the CPU Checkout process which does.