From the results of a quick search it seems to be an evergreen issue though it hit me only once (with 9.33) before today.
Today it rebooted 3 times: 2 times the instant I selected "Go To" in Navigation -> Favourites and once during the activity, forgetting the distance I walked so far and the pressure data altogether to this point.
According to fixlist for 11.28 "Fixed potential shutdowns starting or during an activity." was probably supposed to fix this issues but maybe isn't a full success so far.