Hi their Frank.  I have seen this behaviour on the CAS 4 satellites.  I use Gpredict and had to modify the code so that I could retune the transmitter to get the down link where it should be and then re-lock the Tx and Rx frequencies so that I can tune around.  I just assumed that either the onboard rx or tx had drifted slightly and this was “normal”.

73 Wil – G6WQN