Since you have 3 boards. You know the issue is in the board itself. The 2 and 3 probably had a bad firmware on the 8u2 or 16u2 or they are just broken. It seems 2560 is having more problems than other older boards in this areas.
Since you have 3 boards. You know the issue is in the board itself. The 2 and 3 probably had a bad firmware on the 8u2 or 16u2 or they are just broken. It seems 2560 is having more problems than other older boards in this areas.