Thanks for your answer.
My original error didn’t pop up any more after I upgraded my system. Not a single change in the code.
If I print the shape of the data with batch_size = 1 its [3,64, 128]
with batch_size = 4 the [3, 68, 522] so not exactly 4 times more. And the fact that its a 3 channel not just 1 channel. But that I will try to change directly from the source of the data.
What I’m getting now is the error:

RuntimeError: The size of tensor a (2) must match the size of tensor b (4) at non-singleton dimension 1

when I change the batch_size to 2 i will train (extremely poorly loss starts at 0.011) but at the end of the program I get the same error again with tensor a (6) and tensor b (2)

RuntimeError: The size of tensor a (6) must match the size of tensor b (2) at non-singleton dimension 0