The FRAME_ECCE4 primitive is reserved. This primitive is used when implementing the Soft Error Mitigation (SEM) IP.
The FRAME_ECCE4 primitive in UltraScale+ devices is different than the FRAME_ECCE3 primitive in UltraScale FPGAs. The FRAME_ECCE3 primitive does not migrate directly to the FRAME_ECCE4 primitive, but the SEM IP generated for UltraScale+ devices is designed to use the FRAME_ECCE4 primitive automatically.