ADF4360-1 loss of lock

Good day.

I'm using a ADF4360-1 evaluation board  to clock a AD9739 DAC. I easily lock it at 2100 MHz by sending the 3 24-bit register as required. But sooner or later, the part ends by changing the output frequency, which means that my entire design stops working.

Is that a normal behaviour?

How can I put it back to 2.1 GHz in the shortest time?

Thank you for your support.