I tested it here on my iPad running iOS 9.0.2 for over 10 minutes with about 40 repetitions and had no issues. We also use the SM watch for our Steel Challenge matches and did not have any issues. Those events usually go for about 6 hours.
I have seen a SM watch that had an issue maintaining a BT connection. It was sent back to DAA for analysis.
As for the other one not connecting, it probably had the BT connection flip. When that happens, we recommend plugging the SM watch into a USB power source for 10 - 20 seconds. That will “soft reset” the watch. After that, try turning the BT back on, connecting and then transmitting times. What we have seen happen is if the iOS device goes to sleep for a few minutes, it and the SM watch loose connection. Most time it will “restore” the connection, but on rare occasions it does not and the BT “flips” (for lack of a better term). It will show that it is “connected”, but will not transmit times. The soft reset fixes that.
Also note that the SM watch will turn the BT “off” after 5 minutes of no activity and would have to be re-connected.