Good call, @shama - I had completely forgotten that video due to travel-lag.

You're right there guys, I think this is more a case of the device hardware not coping well with what it's being asked to do. Have you considered rooting and using an xposed module to do the job instead of the unlock app? Unlock app is really only for those who can't root their devices for whatever reason, it runs entirely in userspace and is therefore extremely limited by comparison to another app running on a rooted phone.