The rollers on the bolt are out of spec. Larger rollers can be installed which get it back in timing. The first sign is usually more recoil to the shooter. As the parts wear more and more, the buffer or bolt can be damaged. Some bolts are actually out of spec, milled too much on the face. If larger rollers wont fix the issue, it generally has too short of a bolt. Since the cetme and g3 were spawned off of the concept of the mg 42 bolt, as the other gent stated they can have similar problems.