I guess you might load the wrong checkpoint, since your model’s state_dict can be stored and loaded successfully:
class MyModel(nn.Module):
    def __init__(self):
        super(MyModel, self).__init__()
        self.lstm = nn.LSTM(
            input_size=12, hidden_size=6, num_layers=3, batch_first=True)
        self.linear = nn.Linear(6, 2)
        self.output_layer = nn.Linear(2, 1)

model = MyModel()
sd = model.state_dict()

model = MyModel()
model.load_state_dict(sd)
> <All keys matched successfully>

Are the unexpected keys familiar looking? E.g. did you use mapping and timeLayer in another script, which might have overwritten the needed checkpoint?