Remote TV App not able to see personal media

I am running my Plex server on my Synology box. I have the latest DSM and Plex Server versions installed.

The media I host on this setup has been accessible remotely via TV apps, AppleTV and iOS devices for several years.

Over the last couple of weeks, two of my family members have advised me that they are no longer able to access my personal media; it is still listed but with a warning triangle on it.

In both locations, access is still working on, for example, an iPad. So this issue is very much focused on the TV itself; both are Sony TVs.

Any thoughts would be very much appreciated.