I have no idea what I did, but GPIO16 behaves weird. There is a transistor that allows me to toggle the cols with one pin. PIN 16 "OFF" weirdly jumps between HIGH and LOW, but I neglect that because you can achieve the desired state by just pressing the button longer.
Like with many of my projects there is no backside yet, but this is so much better than having the pure PCB flying around.
An external antenna could be handy, at least a 17cm wire or so.