If users are being removed from groups that you have manually created it's a good idea to check the following.
1. Is the group status protected?
Our provisioning service will suspend any groups that are not in the MIS feed.
2. Are the members locked to the group?
Our provisioning service updates users group memberships and removes them from groups they are not listed in from the MIS feed.
To resolve this protect the group status and lock each individual member to the group.