I've had & fixed that issue on a couple cars. Recently there was a discussion about buying the VW part (latch mechanism) to fix it much cheaper than the Boxster part. (Just be sure to get either the 8 or 9 pin electrical connector as needed.):
VW do latch/actuator
There is a part in the mechanism that rotates to latch and unlatch the door. That part pushes on a micro switch to let the Central Locking Unit 'know' when the door is unlatched.
On both of mine the rotating latch was made of metal with a plastic coating and the plastic had worn off in the part where the micro switch should contact it.
If you DIY, here's the tech article at Pelican Parts:
Porsche Boxster Door Lock Mechanism / Door Handle - 986 / 987 (1997-08) - Pelican Parts Technical Article