The third chip that I got from ISSI is IS31FL3736. It's very similar to the IS31FL3733, except it only drives up to 8×12 LEDs. That's perfect for those 7×11 LED matrices that I got!
I actually designed that shield a while ago, and assembled it when it came. But it didn't work, at least not reliably -- the chip would sometimes be visible on the I²C bus, and sometimes not, and sometimes it would start behaving weird after some time... I put it all to my poor soldering skills and the really tiny QFN package, and gave up on it for a while.
Yesterday, after debugging some problems with the IS31FL3733 on the #PewPew FeatherWing, which were solved by adding a decoupling capacitor across the power, I decided to dig out the old board and try adding a decoupling capacitor to it too. And what do you know, it works perfectly fine after all!
The PCB is here: https://oshpark.com/projects/luMANBrm
And the updated MicroPython library for driving it: https://bitbucket.org/thesheep/micropython-is31fl37x/src