Bettery level drops from 30% to 0% while the battery still has near 30% charge

[TroyInAnatolia]

My HP spectre x360 laptop is two years old.

I always charge until it is 100% full then keep using it on battery only until the battery gets to 10% giving me a warning and 5% where it hibernates
(according to my power settings).   At this point I plug in the AC adaptor to charge again until full.

With my average usage (no video games but basically office use and internet use with occasional youtube), the battery lasts around 6 hours I am glad that this has not shown any significant sign of deterioration since I bought the unit.

After I upgraded to Win 11 about two months ago, I noticed something strange:
- Once I turn off my laptop while the level is still around 30% and try to turn on again after a while, my laptop starts booting and once Windows takes control,
it goes to hibernation and I am unable to boot again.

In order to see if the battery is really dead, I plug in the AC adaptor, turn my laptop on, wait until Windows take control and observe that the
battery level is 0%.
At this point I remove the AC Adaptor and notice that I am able to use my laptop normally for as long as the real remaining charge would allow me to.!
That is, lets say if the level before I shut down was - say 28%, then I am able to use my laptop for nearly two more hours while the power level keeps showing 0%.

Windows is not hibernating or shutting down because the 5% level is already passed and there is no action in the power settings defined for 0%.

With this trick (plug it in, turn on, then plug out and continue using) I did several tests and timed it : 

The total amount of time I am able to use my laptop on battery is about the same as before.

If I never turn the laptop off after the level goes below 30-40% and keep on using it, then I am able to use it for at least three hours and I observe a gradual
decrease in the power level as it did before. Everything works as expected, again with a total amount of time as above.

I've run the battery test as recommended by HP,  by going to BOIS and running the memory test forever until the battery is exhausted and the test passed OK.

This problem is now ongoing. Could it be a sw bug since the battery performace is so good?