PyTorch BetterTransformer issue with coremltool converting


I convert a PyTorch transformer BERT model with coremltool into a .mlpackage model and deploy it to my iOS device. This works well so far.
When I try to optimize the PyTorch model with BetterTransformer.transform before, the conversion process to the .mlpackage model fails with the following error message:

PyTorch convert function for op '_nested_tensor_from_mask' not implemented.

Has anyone had any experience with this so far?

Many greetings!