Do they operate when you use the roof access mode from the dash? if so I would say it would point to the anti-trap kicking in and it is sized.
You can check one at a time by releasing the step from the step board with 2 hex bolts at the rear and see if it moves freely.

The front is not connected to the motor so should swing freely 2017 SDV8 4.4 silicon silver AB
2012 TDV8 4.4 Stornaway Grey AB
2011 TDV8 4.4 Buckingham Blue
2012 VW V6 3.0 Tougreg