I have been on Windows 10 for some time, but my contacts were imported into Windows Live Mail from Windows 8.1 and earlier.  For some time I have had serious problems with Groups.  When selecting a Group for a new email, usually many of the contacts in the Group do not appear.  Also the list of contacts within the Group keeps losing contacts.  For example a Group with 14 contacts gradually drops down towards zero, and does this again when I re-populate it.  What is wrong, and how can it be rectified?

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