Question Two screens, screen 2 canvas buttons are mapped to screen 1

Hi,
I'm using two screens both have buttons. They work fine in editor. However in build screen 2 does not detect screen 2 buttons being pressed. However if I click the location of screen 2 buttons on screen 1 then the button action occurs. So in build screen 2 events are mapped on top of screen 1. I've tried with a single general eventsystem, then created two event systems and made them children of their canvas. But I get the same outcome. I've also tried making eventsystem screen2 first selected be connected to button list screen 2, but this made no difference. Can anyone advise how I can get buttons on two screens working? Thanks. (tried gui forum but no answers)

I'm using unity 2021.3.1f1 on Linux Mint.