You used an unsupported, although reliable method of determining the destination Symantec Endpoint Protection Manager (SEPM) client group for newly installed endpoints by manually editing the PreferredGroup parameter in the Sylink.xml file.
Upon installation, the client would register to SEPM with a manually defined group rather than a group that the installation package was exported from. This allowed for one SEP installation package to be used to deploy clients to different SEPM client groups without the need of exporting installation package for each group individually.
In SEP 14.2 and newer that method of SEPM client group assignment no longer works. The PreferredGroup parameter is ignored.
This issue is fixed in Symantec Endpoint Protection 14.2 RU2. For information on how to obtain the latest build of Symantec Endpoint Protection, see Download the latest version of Symantec software here.