I see the following possibilities or a mix:
-> The recommended register settings have not been used
-> The hardware does not follow the reference design
-> The sensitivity measurement method give incorrect result
- Could you post the register settings you are using?
- I assume that you don't want to post the full schematic/ layout but is it possible to post at least the part from the RF_P/ RF_N pins and to the antenna.
- Have you used the sensitivity method you use in production to measure the sensitivity on the CC1101EM? Does the SG send a CW, preamble or packages? Is the sensitivity determined on RSSI level or package CRC received correctly?