Hi Tchu,
I think that with digitakt 2 the double triggering issue turned out to be something they fixed in a firmware update so it’s going to be hard to determine the exact cause of the problem.
Is it double triggering only when you trigger the track with a trig? Or does it double trigger on the sequencer as well?
I’d check the firmware version and run the error test and keys test. If it acts like it’s double pressing those trig keys during the keys test then it might be a physical issue. If it acts normal during the keys test then more likely software.
I see more than a few reports of this same general behavior so maybe it’s best to contact support again and tell them what you’ve observed, they are probably already aware of why, although I can’t imagine why they didn’t test the device before returning it to you.
What did elektron support fix for you?