Problem with serial communication

[burakkaraceylan]

Hello,

I just built a Klor keyboard but there is a weird problem and I need help to fix it. Both split parts work fine when tested separately. However when I connect them using a trrs cable last two keys (shift and ' in the default layout) constantly registers as pressed. I checked the pcb's with a multimeter and there doesn't seem to be any shorts. The thing is if I dont push the trrs jacks all the way in and leave the last bit out then the problem disappears. What could be the reason?