Issues selecting & moving multiple files

On one of my PCs, when I select files, the functionality in one of my folders is not "normal": when I click a file, and then click another file, the 1st file remains selected instead. And when I go to move the selected file/s, the file/s get deselected when I click on them.
The issue seems specific to this folder within a saved group of tabs. Is there some setting I've enabled that's doing this in this instance?

You're probably in Power Mode rather than Details Mode, and have the mouse buttons for that mode configured for toggle-select.

If it only happens in one folder, it probably has a folder format assigned to it which changes the view mode.