Is it normal for USB-C solder joints(2) back of the MB to be just lightly touching, as they are in symmetry I gather is might be but looks suspicious being so thin/small connection.
USB-C connector pinout here. It's okay to bridge the V+ pins (red A4-B9 and A9-B4) and to bridge the GND pins (green A1-B12 and A12-B1). In fact, the pins are mounted to a common electrical substrate, they're already soldered together underneath. Visible solder bridges on the topside won't open/short any electrical paths unless they bridge other adjacent pins, they just look sloppy.