According to UG-109 when using an external reference for EVAL-ADF4350EB1Z:
...disable the on-board TCXO by removing R1 and R2. R9 can be populated with 50 Ω to adjust impedance matching...
However, looking at the schematic R1 and R2 are not associated with the TCXO.
I think this might be an error - has anyone used the external reference and made the modification?