During scripting, combination of shape (or size()) and slice (e.g x.shape[2:]) produces following error:
slice() missing 1 required positional argument: 'step'
This happens because aten::slice has 2 signatures:

• aten::slice(Tensor self, int dim, int start, int end, int step) -> Tensor
• aten::slice(t[] l, int start, int end, int step) -> t[]

and when a list is passed instead of tensor the 2nd of the two slice signatures is called, and since it has 4 instead of 5 arguments it produces the above exception.