[quote]
If the mass reaches the bottom of the loop for the first time, the arrow of the centripetal force and normal force become suddenly twice the size they had one step before.
[/quote]
The curvature of the trajectory changed when the mass reaches the bottom of the loop,
i.e. the radius r for the circular motion change to a small value so the needed centripetal force become larger. $F=m\frac{v^2}{r}$.

[quote]
After the loop the normal force shrinks suddenly
[/quote]
After the loop, the normal force equal to the weight mg of the object.
While in the loop, the normal force equal component of mass in the normal direction, plus centripetal force.
[quote]
After the first 90 degrees the normal force suddenly shrinks almost to nothing.
From here 180 degrees later the opposite happens the normal force grow suddenly to the size of the centripetal force.
[/quote]
Yes. there seems to be a bug between 90-270 degree. The normal force should equal to component of mass in the normal direction, plus centripetal force. I will check it again and update it soon!

P.S. The simulation has been updated.