There are different ways to save the parameters and each has its own advantage. I havenot used all of them so I cannot explain about all of them. However, I use
torch.save(model.state_dict(), 'model.pth.tar')

To save the code  and
model.load_state_dict(torch.load("model.pth.tar"))

To load the parameters
maybe .pt has its own way to load or is incorrect format(I am not sure).
If you can retrain the model then use the given code to save and load the model. I hope it will solve your problem.