There's a really bad batch of Chinese 20W bulbs doing the rounds
(assuming 12V?).
It's not a problem with the bulb pins or fitting holder *contacts
(although some fiddling can get it lit again), it's a fault in the
bulb itself, where the filament is badly spot welded to the connection
wire inside the glass enveleope. Heating and cooling *exacerbates the
problem until *failure.
Aldi are doing packs of 20W spares at the moment.

No it is nothing recent - I've had these lights for about 3 years now,
and daughter has been at uni in this time which is why I maybe haven't
raised it before. Not down to chinese bulbs.