I can’t give you an answer, but just a few questions:
Are you sure you are running exactly the same code that previously worked?
If so:
are you getting exactly the same output, including that warning about not using all the roberta parameters?
(That’s a lot of layers not being used.)
has your data been changed?
has the colab environment changed - for example, is it the same version of transformers?
What is the loss function value before you start training?
What would you expect the loss to be showing as?
Could it possibly be training completely within the first epoch?
Do you still have a notebook (with output) that shows what used to happen when it was working?
Is your Colab Runtime set to GPU or CPU?
Finally: exactly when did it stop working?