Ok I've been trying to figure this issue out, but couldn't, so here it goes..
Firstly firmware versions are:
1 x DS-KH9510-WTE1(B) - v2.2.36 build 240115
2x DS-KD8003-IME1(B) - v3.7.1 build 250317.
Now the issue: when someone rings the 8003, the video stream doesn't load in hik connect and I also get the error code notification. I have checked time settings and video format is H.264.
Any ideas ?