Per SADP those addresses appear to still be correct, but SADP reports what IP is statically set in the camera, not logically where it resides. If DHCP gives it away to something else, as you said, it's going to be flakey. Some packets will go to the cam, some will go to the mystery device.
The pages you're seeing is likely stored in cache and not actually being fetched from the camera. Make sure you try CTRL+F5 to refresh the page. This forces the browser to retrieve the entire page from the server (camera) and dump it's cache. At this point, if it idles or times out and throws an error, you know the camera doesn't reside at that address anymore because the computer didn't get a response.
If you have a smartphone or tablet and wifi as part of your network, I would suggest downloading Fing. Fing is a GUI version of a popular Linux tool called nmap that scopes out everything on your network and gives you lots of info on devices on said network. It should be able to identify devices with multiple addresses and addresses assigned to multiple devices. It lists manufacturers too so it'll help you differentiate Hikvision devices from everything else. If an IP conflict is truly the problem (seems probable) Fing should be able to pinpoint it.
To resolve the issue, get the MAC addresses of the cameras on your network and in the router add them to the static DHCP section/reserved IP list (could have other names). This registers those IP/MAC combos with the router so the DHCP server knows not to give them away to anything but the camera. Alternatively, start your IP range at something like .10, then .2-.9 are reserved addresses to set things statically with. That will eliminate the DHCP problem completely, regardless of how you do it.
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