Curious if you were ever able to figure this out. I’m getting your error and an additional one when using Nvidia’s APEX library for mixed precision: 'std::out_of_range' what(): vector::_M_range_check: __n (which is 671091489) >= this->size() (which is 3). I’m training a 3d network for segmentation in pytorch and due to GPU memory constraints, I am placing all activation computations in GPU1 and loss computation in CPU. GPU0 takes care of the rest.