card not found under VPN (Tailscale)

I have this simple card, in HA running as a docker container, that works perfectly on WiFi. However when I'm away from home and then on tailscale VPN the card cannot be found.
I thought this might be the VPN but there are no issues or logs that indicate a error.
All other cards and custom cards work fine. All other HA functions are perfect.
I installed this card from HACS.
Could it be that this card is using a resource that isn't visible inside a VPN for some reason...as I say all other HACS custom cards are fine so I'm using inverse logic to remove HA, HACS, WIFI, VPN, as the root cause, which only leaves this card / setup
?