Once set up group submission, later deleted but students still can't submit works individually

[YupingLi]

The first assignment is an individual one and the second is in a group of 4. I set up groups for the second assignment before the first assignment's due date, and the group setting applied to the first assignment submission! As the result only the first group member's work was shown on Canvas, other students can't upload their works.

I deleted all the groups settings once I learnt the problem with the submission, but the problem remains.

Can anyone help?

Thanks!