Are on a laptop? I keep accidentally shrinking the type by holding Command/Ctrl and scrolling on the trackpad (2-finger on Mac). You could try that shortcut to scale things back up.
I've tried scrolling to zoom, as well as holding CTRL, ALT, SHIFT etc. while both scrolling and pressing + and -. Nothing happens, except for when I do CTRL+ and - to zoom the browser's view, but that still doesn't fix the problem of UI elements shrinking in Construct.