Hi  @bollingerd  Welcome to the Canvas Community. First, I hope you have figured this out on your own by the time I'm answering this for your own peace of mind, but if not I can virtually guarantee that the reason this occurred is that when you re-opened it for that one student you did it by replacing the Everyone in the Assign to field with just that one student---which, as you have seen--effectively removed the attempts from everyone else!

The "trick" when doing this in the future--and to solve your situation--is by clicking the +Add button underneath the assigned due date/time for that one student, which gives you a second Assign to field which should be assigned to Everyone Else.  Once you save the quiz again, presto, the missing grades will re-appear.  This solution, by the way, is visually outlined here:  https://community.canvaslms.com/docs/DOC-26363-how-do-i-assign-a-quiz-to-an-individual-studentunder the Add Additional Dates heading.

I hope this helps, David!  Be well!