I recently purchased an FR965 and am very frustrated with the sleep tracking.
1. You need to edit your usual bedtime and wake-up time.
I work at night every other day and when this happens the clock goes into sleep mode in the middle of my work. If I don't configure these times it doesn't track sleep automatically.
2. I worked today and slept in the morning, now it's 4pm and the clock understands that I'm still sleeping, even though I'm already active.
My old FR245 was infinitely better in this regard.