Always on Display seems to turn off randomly

A week ago, I turned on low-power mode because I couldn't charge my phone for a while. After this, when I turned low-power mode off, I noticed that Always on Display sometimes turns off immediately or some minutes after being locked. It happens specifically at 6 PM. I know that it could turn off when it isn't used and it could be my pattern like three weeks ago, but I'm sure I've been using it 6-7 PM last week, so I

don't know how it learned to turn off.

Also, it turns off when I sit in a dark room for like five minutes. I don't know if I didn't pay attention before or if it's a new issue.

Maybe I'm overreacting but I'm concerned about this one, to be honest. I haven't experienced any problems with this feature since now and I really like iPhone's AoD.

For context, Always on Display is turned on in the Settings. I don'town an Apple Watch. Any other functions seem to work properly. I've been using it for half a year now and it has 96% battery capacity

currently.