After upgrading to SW 2019 SP3, I've noticed when I use the "Closed Corner" feature and flatten the part, I have this strange cutout. I've tried adjusting the settings I figured would cause this and can't figure it out. Any help would be appreciated.
If you look at the flat with the bend lines, you can see that you need that cut there for the part to be able to fold.
I unchecked "Merge Faces" in the flat pattern feature and now you can see the bend lines. You need that rip for the corner to be formed with the two flanges.Depending on who is programming the flat pattern, they may change the relief there to work better for their equipment.
It's not the closed corner causing this. If I suppress the closed corner, this is what the flat pattern looks like.
Good luck,
Carrie