Paul Minors said:
I tested with a new user account and it worked. But still doesn't work on my account.
Perhaps the issue is specific to the User Account ScreenFlow Preferences.
In the problem User Account:
Hold Shift and go to ScreenFlow > Help > Gather Support Diagnostics and use the Reset ScreenFlow.
If the issue is ScreenFlow that would fix it.
It started working again. After leaving it a few hours I came back and it was working.
I see in this thread that background maintenance scripts could be causing an issue. Although, I've never had an issue like this with other apps. It seems crazy to me that an app won't open for a few hours because the Mac is performing routine maintenance tasks.