Workflow failed with this error:
Failed to cache field with id “{blah-dae2-4908-80cd-blah}”, overwrite=0

In my list (A) I had a lookup column pointing to another list (B). In B, I had updated a field from Single line of text to Multiple lines of text. The workflow did not like this update. Once I recreated the field as a Single line of text, the workflow started working.