Please ls -al /home
And note this from man usermod
-G, --groups GROUP1[,GROUP2,...[,GROUPN]]]
A list of supplementary groups which the user is also a member of.
Each group is separated from the next by a comma, with no
intervening whitespace. The groups are subject to the same
restrictions as the group given with the -g option. If the user is
currently a member of a group which is not listed, the user will be
removed from the group. This behaviour can be changed via the -a
option, which appends the user to the current supplementary group
So I think you might have messed up the groups for the users A M
What is the output of groups
when run as user A?