This conversation has been merged. Please reference the main conversation: Photoshop CC 2020: Layer Effects on Groups Clipping Error
I was grouping some smartphones for an AppStore entry when I noticed the semitransparent square in the upper left corner which was caused by the shadow layer effect I placed on the group.
The was nothing painted in that area and even masking the whole group did not remove it. I could avoid it by removing the shadow from the group and apply the shadow to an element inside the grouped elements.
I never noticed this in Adobe Photoshop pre 2020. I tried to illustrate my experience with the picture below.