We rarely use multiple attempts in assignments (we usually just set one, but allow manual reopening. But something similar happened once when we allowed a 2nd attempt. It turned out that the comments and rubric settings were still there, but in the first attempt. I recall there was a bit of red text with a link to switch to the other attempt. Everything was still there once I found that link. Since there are no settings in assignments to take the highest grade or other for multiple attempts (like quizzes do) it seems Moodle just treats an additional attempt like the first one, with a blank grading page.
Could this have been what happened?