t looks to be maybe a flushing or state issue; I’ll check into it more and see if I can get a proper fix but I have a workaround you can try.
Create a UMG widget and add a tiny border in the upper left corner. Set the brush color alpha to 0.01 so it isn’t visible. Create and add it to the viewport in your level blueprint. This will make sure it renders something last. This cleared up the problem in our testing.