My 2009 did exactly what you are describing. Another symptom is that can't change from R to D in one pull.

There is a position sensor inside the gear selector unit that is stuck. Open it up and put a little white grease in there. Make sure the two position sensors both slide smoothly before closing it up again. Once you lube it, the gear selector will work fine again.

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2003 4.4i black ext./black int./black headliner (kid's runabout)
2014 535d X-drive, M package, silver/black interior

Sold but not forgotten:
2009 E70 35d, black ext./black int./black headliner (sold 2021)
2006 4.8iS Le Mans blue/cream int./black headliner, SOLD in 2012 sadly...

Other hardware:
2015 Cayenne S (wife's new DD and definitely wroooommmmm)
2016 Tundra 1794 edition crew cab, luxo hauler
2005 Tundra crew cab, weekend hauler. Sold after 150k very happy miles.