Wheels coming of a urban trailer

Morning all

We recently have had wheels come of a trailer on the near side on a single axle urban trailer used for beer delivery (dray vehicle ) it seems the hub is become detached causing the wheel to come of we think this is a manufacturer fault this has happened to several vehicles has anyone any knowledge of this or anyone has idea why this might be happening yes the wheels must be re torqued if removed
It would be most helpful please