This morning we swapped the LNFS that generates the 22.3 MHz used for IMC longitudinal and angular controls with a DDS. 
This LNFS is the one with the communication problem. It will be sent for repair. 

When resetting the output frequency and amplitude of the DDS to nominal values the IMC relocked and so did the RFC. 

We checked some INJ signals : IMC and RFC error signals, 22 dfreq, IMC OLTF... and everything seems to be ok (figures attached)