I have had this happen a couple of times now, I shall try to replicate again this evening, but on both occasions the same process caused the issue.
Starting from the runway with engine already running. Parking brake is set to on, and I spend around 5 minutes toying around with the GPS, lights, tablet etc. getting ready for the flight. Then I release the parking brakes and nothing happens. Now the really weird thing is I can increase throttle and the plane remains stationary, but if I touch the toe brakes, the view in the virtual cockpit moves forwards to simulate the effect of slowing down, release brakes and the view pulls back simulating acceleration, touch brakes again and I get the slowing down/deceleration effect. Nothing I do gets the plane moving at all so I generally have to restart the flight. Has anyone else experienced this?