I had the same error and I don't know if my situation is related but this may help someone else who searches for the same error.

I was able to resolve this error by creating a new Pipeline, using GitHub as the source and the same repo that was referenced in the broken pipeline, and re-authorizing the repo access in the GitHub prompt. I stopped there and didn't finish creating a new pipeline because after going back to the original pipeline in a new window, it was working again.