Small box appearing on layer masks on the bottom right hand corner

On

Photoshop 25.1, there's a small box appearing on the bottom right-hand corner of layer masks which are a bit annoying even though they don't affect in any way the functionality of the program. But it blocks the view of whatever you're doing on the layer masks. The beta version has a way of disabling this issue in the layer panel option area via a check box. This check box option is not on the release version.