adj., what you have found is the head of the screw and washer used to secure part of the cooling unit chill plate to the back wall of the freezer. When originally installed it was probably over torqued and when the temperture changing back and forth from use and non-use or defrosting has fatigued the metal in the fastner. If you are only missing one it should not be a big deal. To repair you would need to drill into the center of the screw and use an easyout to back out the remaining screw and install a new one.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7