I purchased this split keyboard kit called a gergo and assembled it myself. The board properly registered via usb so I flashed it with qmk which has very good support for atmega32u4 and several existing layouts for the gergo.
I have an issue where intermittently (every 5-30 mins), random key input gets sent from the board, BUT only while I'm typing. It doesn't happen if the board is just sitting plugged in. It appears to be only the LEFT half of the board, and a handful of keys. Usually disconnecting the left half TRRS cable and reconnecting it resolves the issue. I beleive this is an issue with my solder job on the board or a messed up component but I don't have a lot of experience with electronics to know where to start.
The board is 2 halves, each half has 25 diodes (one for each mech switch), the right side has the atmega32u4, the left has an MCP23018 IO expander. The right also has a few capacitors, resistors, and an oscillator.
attempts to fix
I put extra flux and re-soldered the IO expander and atmega chip, but this did not fix the issue. On the software side, I've tried 3 versions of avr-gcc, many different layouts, versions of qmk, etc. That plus the fact the error comes from the left-hand only lead me to believe it's a hardware issue. I've tried different cables (trrs and mini usb).
I have several pictures of the board at various states of build if that helps. Any tips on where to look would be appreciated. I should note that the seller of this keyboard has decided not to respond to any of my emails.