While working on one PowerApp, I observed that the code written in first screen “OnVisible” event is not executing which means OnVisible event is not firing. I found couple of workarounds for this issue.
Workaround 1: Add a welcome screen with a simple button which will navigate to your actual screen.
Workaround 2: If you don’t like the Idea of having a welcome screen, you can use this one. Place a timer control on the screen (make it invisible and sent to back) and write the code in “OnTimerEnd” event.
Properties for Timer Control
Hope it helps to solve this issue.