LMH1229: LMH1229 LOCK_N pin problem

Part Number: LMH1229

I'm encountering an issue with the LMH1229 while receiving SDI signals. When the upstream SDI source is power-cycled, I can confirm that the SDI signal recovers correctly. However, the LMH1229 LOCK_N pin fails to assert low, and the video output from the device is abnormal. Notably, this behavior is source-dependent; with certain generators, the LOCK_N pin does return low after a power cycle. What could be causing this?