Hi RayKi! Thanks for your collaboration! ^^
The object leaves from an one frame animation to a real "5 looped frames" animation long after the scale effect has been executed.
I put the scale effect in a group, that is activated at the start of layout. Then the effect isn't under the condition "Every tick".
Object: Set Size
Addendum: Even maintaining the object actual size with a boolean instance variable before the animation execution, the problem continues.