Yeah, I'm having the same issues with Drum Sequencer and other pattern devices in the Rack plugin doing the same thing. Starting in the middle of the first pattern, or playing the first beat of a pattern after it's supposed to stop. This is something that Reason Studios seriously need to get a hand...

Since today’s upgrade: I am getting an issue where the first couple of beats do not play when using the Drum sequencer in pattern mode. The issue seems to show up when the pattern returns to the start.