Vodacom SA have resolved the issue. The cause was a hanging system process in their environment. They are working on a permanent fix for this error. We have resubmitted all affected messages at no cost to our clients.

Vodacom SA is returning the same custom error code as on 12 April 2018 resulting in an "UNDELIV" status for a small portion of outbound messages. Vodacom SA are investigating and once resolved, any messages with the incorrect status will be resubmitted at no cost to our clients.