I have been modifying arducopter code (2.9 and 3+) for awhile now and just recently ran into issue with the bootloader on several apm 2.5 boards. I use linux for development so I use command "make upload" to upload the hex files. On all three boards it makes it 99% the way finished on verfying hex before it bricks and stops. This causes bootloader issue on next power which makes me have to use avr programmer to upload the bootloader again. I'm just trying to figure out what causes bootloader issue..is it an error in the code or is just bad luck. Another weird issue is that once I fix the bootloader issue I can't use "make upload" command again even with standard vanilla code due to stk_error issue but I can upload firmware via mission planner. Any help/tips would be great!