Resolved this myself. It's a bug in Chromium, doesn't happen after the very latest version or on Firefox on the same machine. Pi4 makes an awesome remote monitor. Now if only I could make sense of camera ordering logic...

Hi Guys Been working on this site for a while and they have a couple of Pi4's dotted about that act as remote monitors via chromium and UI3. All was working well till I setup substreams the other day. Now it all *seems* to work until you full screen when it becomes pot luck which camera you'll get. ...