Automatic low power mode

I'd like to understand, with certainty - what the expectation is with Low Power Mode

To my recollection, low power mode has always automatically engaged when the battery drops below some threshold (20%)

I've recently discovered (currently on latest iOS 18) that it is no longer automatically engaged, though I do get a brief notification in the dynamic island

This article (1) seems current for iOS 17 and iOS 18.. It states:

"Low Power Mode automatically turns on when the battery level is low and automatically turns off when the battery is charged to a certain level"

This article (2) has no mention of it being automatically engaged

This article (3) states:

"Your iPhone lets you know when your battery level goes down to 20 per cent, and again at 10 per cent, and lets you turn on Low Power Mode with one tap"

I also see reports from various people (over a number of years) about this issue, and that setting up an automation is a good workaround, while it does not seem to be the case for everyone. There could be discrepancies between iOS versions and device models, and maybe a change in functionality.. so who knows.

Further to that...

I've spoken with Apple Support, and they have assured me that it should be automatically engaged. They've also advised me to variously:

a) Try manually enabling it, restart the device, manually disable it.. and see what happens (didn't work)

b) Try to "Reset Settings" on my device (haven't tried)

c) Factory Reset and recover from a backup (haven't tried)

Finally, Apple Support ran a diagnostic on my device which reported:

a error on iPhone Mid/Rear System Compatibility Check

I was advised to make a Genius Bar appointment on this basis.

The apple store greeter told me that her phone no longer automatically goes into Low Power Mode and recommended setting up an automation (as I've seen others suggest).

The Genius Bar told me his phone has *never* automatically engaged Low Power Mode, his experience has only ever matched the description in article (3)

Finally, the Genius Bar informed me that "iPhone Mid/Rear System Compatibility Check" is not an error per se, and is essentially meaningless (that it is intended as a reminder for whoever might be servicing such a device). I'd love to get some clarity on that. Is it a potential fault or not? Do all iphones of certain models report this wether there is a fault or not?

I have an iPhone 14 Pro (running iOS 18.0)

To summarise:

• Apple documents disagree on expected behvaiour
• Apple staff disagree on expected behaviour
• If it's a bug, how should it be reported?
• If it's a documentation issue, how should it be reported?
• Should "iPhone Mid/Rear System Compatibility Check" be investigated?

I won't take any further action until I can confirm if this is indeed a bug or an issue with my device specifically.