Public server WSS:// for networked games

Hi all -

I wrote a party game with networked code to show on four screens for my son's birthday. Exported the server to a public server with LetsEncrypt certificate. Upgrade headers are set, etc.

This works fine on desktop.

On a mobile browser (both wifi and 5G) the connection is dropped immediately. Are mobile browsers just stricter with cross-origin WSS?

Do you know anything else that could cause this?

Thanks in advance - relet