Probably the same reason I've got a 4 channel cctv recorder with 4 cameras connected, but it will only play nicely with 3 of them.
I've rebooted all the cameras one by one, and even all together. They all work fine on their own. No different. there's always one that won't show properly.
Thing is, cos there connected to the wifi in the house as well, all 4 are always visible and behave on my mobile, either via wifi, or my mobile data from anywhere ????????????