Looks like torch.jit is interpreting nn.Embedding and nn.LSTMCell as python functions. The code and error are below.
import torch
class Model(torch.jit.ScriptModule):
    def __init__(self):
        super(Model, self).__init__()

        self.embedding = torch.nn.Embedding(128, 512)

    @torch.jit.script_method
    def forward(self, x):
        return self.embedding(x)

m = Model()
m.save('temp.pt')

Traceback (most recent call last):
  File "test.py", line 16, in <module>
    m.save('temp.pt')
RuntimeError: Couldn't export Python operator <python_value>

Defined at:
@torch.jit.script_method
def forward(self, x):
    return self.embedding(x)
           ~~~~~~~~~~~~~~ <--- HERE