most of the time I'm looping synced to MidiClock, which works well and stable. The REL SYNC option allows me to start recording exactly at the button press, but stopping the recording is a problem (I mean hitting REC again, but I'm going to call it STOP from here on):
When I hit stop, it records until the cycle is over. So I have to hit stop anywhere before the end of the bar. But as I am more a drummer than an ableton-style clip-launcher, I want to hit stop right on the "1" of the next bar. This means, I have a 50% chance of hitting stop shortly after the "1" instead of shortly before. That means SL is going to record another cycle.
I think this issue is not easy to resolve, as the current sync works mainly by waiting for special sync events. What needs to be done is rounding/approximating the sync event time. This means recognizing that a (rec start/stop) event is closer to the past sync event ("1" of current bar) than to the next one ("1" of next bar/cycle) and adjusting the loop length, state and position in retrospect.