I found an unaddressed bug while working on a inventory system.
I was working on dragging dropping items and noticed when you try to drag items (widgets) in 4.18 they appear more to the up and right where your mouse is. This happens when you Play in Selected Viewport. When you switch to Standalone Game it works fine.
After digging in I found this to be an unaddressed problem in 4.18 (which I was using) as you can see below.
Indeed; when I made a clone of my project and run it with 4.21 it works fine.
This costed me 2 days. I hope this is avoided in the future.