The issue, which surfaced as early as 2011, prevents text messages sent to some former iOS users from reaching their intended recipients. Apple has moved to fix the issue that prevented its support staff from manually fixing the issue for affected users.
Samsung user sues Apple over lost messages after switching to Android
The problem happens when Apple fails to de-register phone numbers from its iMessage database, and attempts to forward texts to iMessage, even if the user no longer has access to the service. In some cases, this leads to loss of messages.