Time sync Issues

[phuoc]

I have a Hikvision NVR with the model number DS-7608NI-K1 connected to 8 Hilook IP cameras with the model number IPC-B121H. All cameras have DST (Daylight Saving Time) disabled and are set to manual time mode. The NVR uses NTP to synchronize time. The cameras automatically sync with the NVR's time and initially show the same timestamp. However, the issue is that after a few minutes of synchronization, 2 out of the 8 cameras lag by 1 second compared to the others. I still don’t know how to fix this. Even though I’ve restored the default settings, the problem persists. If anyone knows a solution, please help me.