In Windows 10, when I have a group stack in Bridge, sometimes when I (left) click the thumbnail, nothing happens. It isn't selected. The thumbnail doesn't show a blue box around it. This happens with some stacks and not others. If I want to move that first file in the stack to another place in the stack, I cannot select it by left-clicking. Instead, I need to move another image in front of it and then select it and move it. But then the new first image becomes stuck "stuck." If I want to open a file, double-left clicking the thumbnail to open the image doesn't work. However, I can right-click and choose OPEN from the dropdown box.
The stack can be "fixed" if I ungroup the stack and then group again, but that's time consuming because I have to rearrange images around in the stack because it's not always ordered alphabetically.