Paths and objects not selecting properly

I have a weird problem I've never encountered on AI before. I've been working on a file for a while, and suddenly today it started not behaving properly when selecting any element.

Basically if I click on a path it doesn't then retain the selection, it only shows the bounding box. Normally it shows the path I have selected with the bounding box. Similarly if I click any object or type, it only shows the bounding box and not the path or type.

It's driving me nuts - I don't know if it's glitching or if I tapped something by mistake? If I copy the entire artboard into a new file everything works fine, so I guess it's not too much of an issue. It just seems to be this one particular file at the moment. Anyone else experienced this?