Faulty mechanical keyboard: Identifying "defective" ground connection on PCB
Good effort, but my hunch is a lifted pad on the row enable from one of these pins.  If you have a 10x eye piece, from a microscope , or really good eyes, you might see something, or press down with a wood or plastic tool gently on pads. or even your finger pressure. 

Otherwise a cracked via or trace may be impossible to find without locating the row enable track on either side.


  An open is more likely than a short here as a short might block all rows.


All it takes is a few "nm" to open from IS and it can bridge with capacitance with scan pulses. ( explaining possibly why restart affected results.)  Otherwise expect ESD damage.... N.G.

Solder defects usually are 98% of all mfg defects and intermittent ones are harder to find.  Usually IS insufficient solder, SB , solder balls , or BR, bridge are the notations we used in Contract Mfg. but large panels can crack vias from excessive warp or improper depanelization stress.



Keep up the good effort. With practice you can fix mine. ( I used to twist some to get working momentary (not recommended)