I bought a new S60 2015.5 model in late Oct 2015, and have been noticing odd intermittent behaviour... Sometimes after I come to full stop at a stop sign or lights (or sometimes when I'm braking while parking in reverse/drive), I notice that when I take my foot off brake the car won't roll forward as it should normally. Rather the car hesitates for 3-4 seconds and then it jerks forward. Feels like the car is locked or stuck before it breaks free.
I also noticed that before the car "breaks free", if I press the brake again it is very hard/stiff.

Days may go by without incident but it can also happen multiples times in a day.

This does not seem normal.

I took it to the dealer, and they test drove it but it did not happen while testing.. They also updated software, but this still is happening.

Any thoughts?