Adding force to a group of particles

Hello!
I am using LIGGGHTS 3.0.7.
I am trying to add a force to the group of particles of a particular type.

Here, what i do:
//create region in which the force should be applied
region field_region block -0.1 0.1 -0.1 +0.1 0 0.1 units box
//define group gg which consists only of particles of type 1
group gg type 1
//trying to apply the force which will try to decrease the speed of the particles
fix mag_field gg addforce 0.0 0.0 +0.3 region field_region

This code does not work.
If I replace gg to all in:
fix mag_field gg addforce 0.0 0.0 +0.3 region field_region
Then everything is OK and force is applied.

The problem seems to be in the group definition.
I tried to check if there are some particles inside the group using this code:
compute 1 gg com
thermo_style custom step atoms c_1[1] c_1[2] c_1[3]

But c_1[1] c_1[2] c_1[3] always show 0 during computation.

What is wrong with my code?

Thank you in advance!

Full code:

atom_style granular
atom_modify map array
boundary f f f
newton off
communicate single vel yes
units si

region reg block -0.36 0.36 -0.36 0.36 -0.05 0.23 units box
create_box 2 reg
neighbor 0.002 bin
neigh_modify delay 0

#Material properties required for new pair styles

fix m1 all property/global youngsModulus peratomtype 5.e6 5.e6
fix m2 all property/global poissonsRatio peratomtype 0.45 0.45
fix m3 all property/global coefficientRestitution peratomtypepair 2 0.3 0.3 0.3 0.3
fix m4 all property/global coefficientFriction peratomtypepair 2 0.5 0.5 0.5 0.5
fix m5 all property/global k_finnie peratomtypepair 2 1.0 1.0 1.0 1.0
fix m6 all property/global coefficientRollingFriction peratomtypepair 2 0.2 0.2 0.2 0.2

#New pair style
pair_style gran model hertz tangential history rolling_friction cdt#Hertzian without cohesion
#pair_style gran model hertz tangential history #Hertzian without cohesion

pair_coeff * *

timestep 0.00003125

fix gravi all gravity 9.81 vector 0.0 0.0 -1.0
fix integrate all nve/sphere

fix surface all mesh/surface/stress file meshes/surface_big.stl type 2

fix granwalls all wall/gran model hertz tangential history rolling_friction cdt mesh n_meshes 1 meshes surface
#fix granwalls all wall/gran model hertz tangential history mesh n_meshes 1 meshes surface

#distributions for insertion
fix pts1 all particletemplate/sphere 1 atom_type 1 density constant 4500 radius gaussian number 0.0006 0.000066667
fix pdd1 all particledistribution/discrete 1. 1 pts1 1.0

#region and insertion
#group nve_group region reg
region bc1 cylinder z 0 0 0.06 0.03 0.18 units box

region field_region block -0.1 0.1 -0.1 +0.1 0 0.1 units box
group gg type 1
fix mag_field gg addforce 0.0 0.0 +0.3 region field_region

fix ins1 all insert/rate/region seed 5330 distributiontemplate pdd1 &
nparticles 7000 particlerate 2700 insert_every 1000 overlapcheck no all_in no vel constant 0.0 0.0 -1.0 &
region bc1

compute 1 gg com
thermo_style custom step atoms c_1[1] c_1[2] c_1[3]
thermo 100
thermo_modify lost ignore norm no

#insert the first particles so that dump is not empty
run 1
dump dmp all custom 1000 post/particles*.mixer id type type x y z ix iy iz vx vy vz fx fy fz omegax omegay omegaz radius
#insert particles
run 50000 upto
unfix ins1