Open SuperSU and go into SuperSU's settings. If you haven't bought the pro version, you will see an option to enable pro features even though you don't have the pro version unlocker. Turn on pro features.
Next, in SuperSU's settings, find the logging setting and set it to log full content then clear the old logs and reboot the phone.
Next, once you have restarted the phone, open Broken Switcher and hit the button to pull images, then hit the write to system button.
Go into SuperSU in the logs area of the app and you should see 4 log entries from Broken Switcher. If you click on them it will show the commands being used by the app along with any error messages being returned.
Take screenshots of all 4 log entries and post them here. They will almost certainly tell why the app isn't working.