I've tried two devices, and bricked both. Presumably the project as is must disable the UPDI pin feature in order to use the pin as an interrupt out. Maybe the devices are now functioning as i2c encoders, but I can't check that right now.
If I'm correct, where does that occur in the code? I'd like to prevent it to verify my IDE and programmer is set up correctly.
I didn't think the UPDI could be locked out without setting a fuse, and I didn't think fuses were set by loading and running code in debug.