Radio frequency RF engineer GSM LTE GPRS 2G 3G 4G tracker

I have a custom GPS tracker with a 2g GSM module from ublox, unfortunately the 2G GSM signal is always low with any antenna I use, the signal strength is always low 20%, on very rare occasions it reaches 40%, I have tried about 10 antennas but it never exceeded 20% I also soldered the antenna directly on the GSM module, tried various sim cards, I even went under the repeater, but it is always 20% -40%, the mobile phone instead has 100% signal, the test was done on 10 trackers, is it possible that some component is missing on the PCB?