ADF4351 reference boundary spur when DIV=1

Hi

I am using the ADF4351 in two of our products and see a problem with the reference boundary spur when the synthesizer is set to 2.2GHz and up (i.e div=1). i'm seeing results of about 30 - 40 dBc when the frequency is set in a way that the loop filter isn't rejecting the ref boundary spur, lets say 2260.01GHz. this is happening every 10MHz or 20MHz depending if the ref doubler is on or off.

I see this problem on both our circuits and on the eval board (EVAL-CN0285-EB1Z).

I am using a 10MHz reference.

Thank you