Best way to isolate RF Coupling (2,4 GHz - 2,5 GHz)
It sounds to me like the power current for the ADF4350 module contains a significant level of RF current i.e. current at 2.48 GHz and this will get onto your BLE board because of the 10-way ribbon connection. What I would do is make a better interface cable that more thoroughly stopped the leak-back of RF currents. You could try experimenting with more ferrites but you might get to the point when you can't fit any more on the cable and then you might need to design a little satellite board that had common-mode and differential inductors on board that choked off the RF from getting back to the BLE board.

If you continue down the ferrite route look for ones that have high losses at 2.5 GHz.

You might also try using some Aluminium foil around the cable and connecting it to earth at the BLE board to see if that stops problems or makes things better when you can't add any more ferrites. 

Sometimes you have to try several things together to reduce the problem to acceptable limits then try removing each measure and see how effective it was. That's EMC a lot of the time.