More likely to be dodgy connectors. Had this problem on a few. Take out the handle and you will be able to see where the connectors have fallen out of the back. Should have said yesterday when you were here, we could have had a look.
Agree. the fitting of the lamp holder into the van is a bit trickly. Make sure that you have enough pre-load on the connections. Also make sure that the connections are clean. I changed my bulbs for LEDs the other day and the connectors were all quite badly corroded.