Royal Mail hub gear problems

Volunteers in South Africa say:

There are quite a few of the Royal Mail bikes in which the rear wheel does not engage when peddling. The rear wheel turns if you are pushing the bike but does not turn when peddling – it seems to stick somehow.

Merlin says:

Please see if the issue is getting the clicks in the gear tooggle switch on handlebars to sync with the gears in the hub, like trigger shift gears needing to be in sync with the derralia cogs.