There is a bug in the joystick library I'm using https://github.com/yoannmoinet/nipplejs/issues/151 that causes the joystick to get stuck.

This only happens in  Dynamic Mode. This is where a new joystick is created on every touch inside the joystick area.

 I've implemented a temporary work around by putting the joystick into Static Mode. It's slightly different but doesn't get stuck. It means there is one joystick inside the joystick area and it's fixed in position. It's also now white. I will experiment more with it.

Thank you for all the reports and that you Nolan for the screenshot reproducing the problem :)