I don’t 100% understand the test mode either… but when I prodded some things in there, most of the buttons had a consistent response but the combos that were causing me issues stood out as responding differently.
I guess this means the buttons are okay and not a hardware issue, but the way the combo information is received is incorrect.
Elektron support claim that it is known and fixed for the next firmware update but no one knows when that will be (assuming your bug is related to mine)