Hi Alex,
A very quick way to debug this is to run this in CPU mode.
You will know exactly why this failed immediately in the CPU mode.
Now if that does not happen, I am thinking it might be a CUDA Unpooling bug, and I want to spend a few hours tracking this down. If you can help me by giving me a script that I can run (with dummy data and stuff) that reproduces this issue, I’m happy to run it and fix the issue within a week or less.