Why did Apple Watch 10 stop providing sleep data?

My wife and I met another couple for a cruise vacation on 3/4. Three or the four of us have Apple 10 Watches which were all purchased in the last 6 months. At dinner the first night we all put our iPhones in "airplane mode" and adjusted the time to manual since we had to turn our clocks back one hour. The cruise was from LA to Hawaii and back. All three of us were surprised that we had no sleep data the next morning. We all tried several things but were unsuccessful in getting any sleep data the whole trip. We had to keep airplane mode on all the time except the daylight hours in Hawaii and we could switch to automatic time during daylight hours in Hawaii. Still no sleep data for the whole trip. We arrived home (in Oregon) on 3/20 and reset the date and time to automatic and with airplane mode off. Miraculously, when we woke up this morning 3/21, sleep data was displayed as it had been before the cruise. What happened to make the sleep data disappear and then reappear?

[Re-Titled by Moderator]