Widgets becoming inactive randomly

I am adding widgets to the sidebars in my site. As I go back and forth to the Widgets page, I’m finding previously added and saved widgets under the “Inactive Widgets” area. I’ve added them back to the sidebar they are supposed to be in numerous times and for some reason, they keep disappearing from the sidebar and appearing under the “Inactive Widgets” area.

Any help would be greatly appreciated. Thanks.