PT650 - Slave doesn't seem to be using DSO hopping capability - Any Clues ?

Greetings to those that know (much more than me) !

We are operating a 51km link that 'sees' more local interference on the uplink than on the downlink (from the master point of view) which limits the modulation mode to 64QAM on the uplink most of the time (compared to 256QAM on the downlink). I have Asymetric DSO enabled (no radar detection here) and the downlink occasionally hops to find a better group of channels (45Mhz modulation bandwith) to maintain data throughput. But the uplink does not hop and appears stagnant even though the link is suffeing byte errors, limited to 64QAM and has adjacent channels with lower interference values. The attached spectrum analysis shows this I believe. Could someone enlighten me why the uplink behaves this way please ?

Thank you in advance for any help on this .. In all other ways the link is running just fine.

Cheers, Peter.