When a keyswitch makes contact, it has a tendency to bounce open and closed repeatedly in a few milliseconds as it settles into place. When this is uncontrolled by software or hardware, it can cause keystrokes to be pressed multiple times.
The firmware currently being used with the early release version (based on StenoFW, originally for Stenoboard) has a section of code specifically to counter this issue by placing a tiny gap of time between when the switch first connects and when it can be pressed again to allow it to settle down into position over those first few milliseconds. The setting is at 20 ms by default, which should be more than enough for any typical mechanical keyswitch to function well. However, I have a report of issues with some keyswitches recording multiple keypresses per hit after about a week of use.
I have four keyboards in the second batch being assembled (and three more keyboards in a third batch printed and waiting to be assembled), so I am going to put these on hold for a short time (days, not weeks) and focus some time on rooting out what the issue is. I am temporarily removing assembled keyboard availability from the storefront until this is solved, since it is an issue that directly affects functionality.
If you encounter any bounce on your keyboard, please let me know and detail if it occurs intermittently on all keys, consistently on a specific set of keys, etc.
Thanks for sticking with the project!