Could you update to the latest PyTorch version? I’m not sure where your 1.6.0 nighly binary would land, but if it’s between the 1.5.0 and 1.5.1 release, note that 1.5.0 accidentally removed device assert statements, so users could run into issues such as illegal memory accesses instead of indexing errors. This was fixed in 1.5.1 again.