Sounds like you may be reading resistance through the switch / diode with it open. Put a thin card between the switch blades and test again, just to take that out of the equation.
Are you sure switch 58 in row 2 isn’t shorting to the diode somehow? check the ends sicking out and that the sandwich insulation looks good and it’s not grounding to the trough plate. check the wiring to the switch is as the other trough switches. Leads from the diode can not cross, or even touch slightly. Band on the diode points AWAY from the white wire.
Yes, I would expect it to conduct 0.5-0.7 in one direction and be open the other way. Make sure you are on a diode setting on the meter looks like ->|. Doing it on ohms or a continuity setting may not properly check the blocking property, as it won’t bias the diode with enough voltage.
Did you do the same check on switch 50? Do you get the same reading there? What about others on that row: sw42, sw34... etc.
Then test diodes with the harness unplugged from header 2J2 & 2J3 on the Driver board. Stick your meter lead in the header for col 8 (green/gray) and the other lead into row 1 (white brown). To avoid harming the connector, I stick in paper clips and wrap them around the meter leads. Even easier to do if you have alligator clips. Press each switch in the row, moving the column lead back 1 position in the connector and pressing the appropriate switch.
So col8/row1 press sw57. col7/row1 press sw49.
I’m hoping you understand what I mean. You’re checking the diode all the way through the harness and switch. You will likely need help finding and pressing switches. It’s harder on your own for sure. Sorry this sucks, but it’s the only way I’m sure will isolate the problem. Look for differences in readings.
In one orientation of the leads, they all read 0.5-.07v approx. The other way around they should all be the same - open or no reading. I’ll leave it to you if you want to swap leads for each switch, or do them all and then swap leads and do them all in order again. I prefer the former.
Afterwards check each switch you got. funny reading on and the soldering and for stray wires for each lead. I just replace any diode I think may be bad, and move on. They cost pennies.