Episerver Cms core 11.13.2
Steps to reproduce.
1) create a page and leave a page property empty (in our instance it's a simple string)
2) schedule for publishing
2) update code to make the empty page property required
3) publish code
4) try to remove the scheduled page
Since the page property is now required you cannot remove the scheduled page because it's empty?
Sounds like a bug to me.
What version of Episerver is this fixed?
If this issue is reproducible in Alloy site then I think you raise this with Episerver Support.