For granular materials, why I have force when connectivity value of this particle is just one?

hello everyone
i am currently trying to study the dumped data from lammps, but i have a really weired problem.
its granular materials with all periodic boundary conditions.
i can identify some particles (very very small fraction of the system) have only “one” contact point, but this contact have force !!!
I do not have the gravity, it is difficult to imagine how a single contact point can generate a force in a system with periodic boundary conditions.If a particle has only one contact point, and there are no external forces like gravity, it is indeed counterintuitive for it to experience a force, as the net force acting on the system should be zero.
does anyone have any idea for this point?
is this a bug for lammps??
the pair style granular is used. thanks all for your help and time

pair_style granular
pair_coeff 1 1 hertz/material 1e8 0.3 0.3 tangential mindlin NULL 1.0 0.4 
pair_coeff 2 2 hertz/material 1e7 0.3 0.3 tangential mindlin NULL 1.0 0.4 

There is not enough information here to provide an opinion. I cannot follow your logic.
The way to disperse doubts, is to provide not just a meager couple of pair_coeff statements, but rather construct a minimal input example that showcases your concern with an explanation of how you determine what is worrying you.