What causes inconsistent nap detection on Apple Watch Ultra 2?

Just got an Ultra 2 recently. Not sure if nap detection is a thing; is it official? The first time I napped, the results only showed up in Heath a few hours later. The second time, it didn’t show up at all. The third time, it showed up immediately as it should in the app. However, I noticed that it’s been a hit and

miss. I had a nap again, and this time there was no log of it. I have to add that each nap is more than an hour long. Can someone tell me what’s wrong? Thanks!

[Re-Titled by Moderator]