I need to do more testing on this but I believe I may have found what could be causing the problem, tough I would not know how to fix it if that is the case.
I have a WIFI extender in my home.
It works by creating a new WIFI network and all devices that connect to that said WIFI use the extender as a bridge to be able to reach the main WIFI router.
To accomplish this, the devices connect to the WIFI extender have the MAC address masked by a new MAC address.
It basically means that a computer is seen as one device when connected directly to the main router and as a completely different one when connected through the WIFI extender.
When the computer that I use to control the Rpi is in the same WIFI as the Rpi itself, I can see the previews without much issue.
However, if the any of those is connected to the network via the WIFI extender, then preview stop work.
It is a bit weird that something like this is happening
If the software conforms to using conventional TCP/IP/HTTP protocols, the underlying structure of the network should not matter.
However, because there is an actual difference when devices are connected to different SIDs, it seems that it may be using some other fancy non-conventional method of communication that is breaking this feature.
I need to do more testing to confirm this is indeed the case.