Hi @MaryJacqueline,

When you're making a due date exception for a single student (or set of students), it is very important to add a new "assign to" and not just replace the "everyone" dates with a single student.  When you add a new "assign to", you'll get a new place to select the student and set their dates, and the original box will change from "everyone" to "everyone else".  If you go back to the assignment now and add a new "assign to", you can select the everyone else option, populate the original dates there, and all of the submissions should reappear. The  How do I assign an assignment to everyone, individ... - Instructure Community - 1191  guide covers most of this info as well.

I hope this helps!

-Chris