The final PCBs for the 8x8 matrix shield based on the IS31FL3728 chip arrived, and I verified that all the connection are now correct and working. You can download the design files and the gerbers in the "files" section above.

Here is the schematic (the connections for the matrix itself are left as ratlines, for clarity):

And here's the image of the PCB (I changed the colors from default yellow on orange):

The bill of materials is as follows:

• the PCB
• the IS31FL3728 in a QFN package
• 3x 10kΩ 0805 resistor
• 2x 100nF 0805 capacitor
• 1x 1µF 0805 capacitor
• 1x 220nF 0805 capacitor
• 1x 8x8 mini LED matrix with anode rows and cathode columns