The clocks start to sync at the rising edge of the SYSREF in JESD205B subclass-1 sync mode. The level of SYSREF at HIGH doesn’t trigger repetitive clock sync.
MAX5871
Production
The MAX5871 high-performance interpolating and modulating 16-bit 5.9Gsps RF DAC can directly synthesize up to 600MHz of instantaneous bandwidth from DC...
Datasheet
MAX5871 on Analog.com