Fully updated iPhone 15 pro screen dimming all the way down while using in bright light.

This has happened a few times now, and I never had this happen with my 13 pro. The phone is fully charged, and not heavily used (warm/hot) at all. I'll be looking at it in bright light, indoors,(at Costco today) and all of the sudden it will become completely unreadable until I go to the slider to turn it up again, as it magically turned itself all the way down. Something is NOT right. I've always used True Tone, I've always used auto brightness, always, and this has never happened. I took 2 screenshots, and both showed a bright screen while it was dark, and unreadable. If it matters..It's in the Apple silicone case, with no screen protector.