Hi @mathor,
what learning-rate did you use for the second lot of training?
Were you using similar training data or very different training data?
Did you save the optimizer state_dict as well as the model state_dict?
This post might help: Checkpoint vs model weight 5
If you load your saved (fine-tuned) model, and do a validation check before you start any more training, what kind of validation accuracy do you get?