One thing that wasn’t disclosed in any of your previous post is that your timer_fnc()
actually is a non-static class method.
That’s why it is important to work on your code not mine 
For non-static class functions you need to use another Timer
constructor
https://docs.particle.io/reference/device-os/firmware/#class-member-callbacks
And in order to actually do that you need an object instance of your Motion_Service
class.
For that reason you cannot have this in your library: Timer timer(1000, MotionService::timer_fnc);
- not even with the correct constructor as you haven’t got an object at that time.
The way you laid out your library I’d rather have the Timer
as a private member of the class and construct and start it in the class constructor.