An endpoint will not change from managed to unmanaged in epo - once it is managed state, even if communication fails, it will still show as a managed agent. If you have unmanaged entries, then that is possibly a duplicate entry. There are several reasons for that.
AD sync creating duplicates (kb89427), agent was reinstalled with a forceinstall (but that would show as a new managed entry), VDI systems without the agent being in vdi mode, etc.
You would probably do best to open a ticket with McAfee for troubleshooting duplicate entries, as there are several causes.
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