Entire battery drained in 3 hours in sleep mode with WatchOS 9 on Apple Watch Series 5 with Cellular

Since updating to WatchOS 9, my entire battery drains in about three hours while in sleep mode.

As you can see in the screenshot, the battery is drained very quickly while in sleep mode at night (00:00-03:00) This is surprising as sleep mode typically uses less battery (and has previously).

I put the watch into sleep mode at around midnight, and by 3AM the watch had completely died. It would only show the time by pressing the side button, as it was in the emergency low power mode.

I didn’t have this problem earlier in the WatchOS 9 Beta, and the problem is present in the final release of WatchOS 9 for me.

This has happened multiple times in the past week: even at full charge, my watch dies within 4 hours in sleep mode.

Battery health is > 90% and it has no issues lasting throughout the day.

I’ve wiped the watch and set it up again and I’m still having the issue.

Can somebody please advise, or log this problem for the engineering team to investigate please?