Server is unreachable but only from 2 clients

Server Version#: v1.43.0.10492-121068a07
Player Version#: 5.94.1 (for Smart-TVs & Plex for VIDAA)
I am having an issue that is only affecting a couple of the clients on my LAN.

When using the plex app on my HiSense smart TV and on my new Manhattan Aero Freely Box I get the server is unreachable message.
It does work perfectly fine when using the plex client on Android mobile, LG smart TV, Samsung Smart TV, Plex WEB etc.
I have tried restarting plex server, no change.

Restarting the windows 11 desktop that runs the plex media server, no change.

Turning off windows firewall completely, no change.

Unchecked Strict TLS configuration, no change.

Anyone got any suggestions on how to resolve this?

Thanks.