Hi @theudster, I ran into just this problem today 
The solution is to change the signature of your compute_loss to reflect what is implemented in the source code 18:
def compute_loss(self, model, inputs, return_outputs=False):
    ...
    return (loss, outputs) if return_outputs else loss

It seems that the example in the Trainer docs is not up-to-date so I suggest inspecting the source code of compute_loss as a reference for now