Synchronization shows all images as missing

Recently I tried to synchronize a folder, and C1 showed all the images as missing. Unfortunately, I clicked the sync button anyway and discovered that all of my adjustments for those pictures were deleted.  I then noticed that most of my folders have the same synchronization issue. 

I'm able to edit the raw files and export the adjustments without a problem.  Is there a way to get synchronization to recognize these files again?