I use RPI Zero W with std RPI OS (and RPI3 ubuntu) and so long as the option LNER (on my Canon 100d anyway) is switch off it runs long exp (over 9 secs) no problem, Dont think the Bulb mod done had any effect on the LNER problem as it was delaying downloading (guess it does more processing for LNER on camera board) that seemed to cause the problem.