Hello Mil2phx,
To help us get a better understanding of the issue, we’d like to ask a few questions.
1. Just to confirm, when the issue happens, does Nightstand Mode appear to have turned back on, on its own, or does it still show as being turned off?
2. Since this behavior started, has the affected Apple Watch been restarted? If so, did restarting improve the issue at all?
The above details will help us plan how to proceed.
To help ensure that Nightstand Mode is turned off correctly, please check out the information in the following link which outlines how to manage Nightstand Mode and may help: Add an alarm on Apple Watch
Set up Apple Watch as a nightstand clock with alarm
1. Open the Settings app
on your Apple Watch.
2. Go to General > Nightstand Mode, then turn on Nightstand Mode.
When you connect your Apple Watch to its charger with nightstand mode turned on, it displays charging status, the current time and date, and the time of any alarm you’ve set. To see the time, tap the display or lightly nudge your Apple Watch. Even nudging or tapping the table might work.

If you set an alarm using the Alarms app, your Apple Watch in nightstand mode will gently wake you with a unique alarm sound.
When the alarm sounds, press the side button to turn it off, or press the Digital Crown to snooze for another 9 minutes.

Thanks!