I can’t help on “why it happens”, but I can tell you why you are seeing 2 different levels :
– one RXLEV is the DL RXLEV BCCH level : maximum power, on 1st TRX (no power control, no DTX)
– second RXLEV is the current DL RXLEV of your TCH timeslot : attenuated by DL PC and DTX, on probably another trx than the 1st one.
2 TRX in the cell might have different Tx Power (either due to configuration or due to hardware problems or due to different feeder systems, different antennas , different orientations, the color of your cat and the size of your car…. 😉 )