Lost all my medals on Campaign missions

I just logged in today to discover that I have lost (almost) all my medals in the Campaign missions.

I have played the entire campaign in co-op and I was always the client and my friend has always been the host. We finished the entire campaign together. We got a few gold and rest were silvers.

The game remembers that I have completed each of the missions because it shows in the Mission Completion section. It also remembers almost all the Optional and Bonus objective completion - it is missing one Optional Objective from Mission 4 for some unknown reason.

The only medal the game remembers is the Gold medal I got for playing mission 2 solo.

I have kept a spreadsheet of all my medals before the data was erased.

Is there any way to get this data back?

My friend and I are working towards getting the achievement for getting Gold in every mission - will this work now that my medals have been erased? Will I be required to get Gold again on the missions that I have already obtained gold?