uGUI Components keep disappearing from the project

Our team has been running on Unity 5 for a couple of months now with pretty good success. One issue we've had since the beginning is that every once in awhile someone in the team will load up the editor and play the latest game in it and the uGUI components will be "Missing" - The prefabs with various components like the sprite component will load with nullref errors because the Sprite component turns into "Missing mono script".

We pretty quickly found the work around: Delete our library folder and rebuild, wasting 30 minutes. It happens once every few weeks to team members at random and we have no replication steps.