Franc Zabkar writes:

Diode array? (A)node/(K)athode?

Yes, good call, thank you. Each chip is two diodes, four leads total. It
explains all the resistance measurements being open circuit, as the
ohmmeter wasn't overcoming the forward voltage drop. Measuring with a
diode tester succeeds.

I think the diodes are either encoding matrix signaling, or perhaps the
pull up/down you mention.