Weird battery drops

Hello there,

I have an iPhone 12 Pro Max, 8 months age. Usually I charge it between 20-80%, 90% of time. Also, battery health it’s still at 100%. The weird thing is that 2 days ago I have noticed something a little bit weird:

-I plugged in from 29% to 32%, have charged very very fast in max 1 min, I have unplugged it and then in max 1 min, percentage dropped back to 29

-few moments ago, the battery dropped again like crazy, from 48% to 44% and also after that, few moments later again, from 30 to 27% in few seconds. Also in this “area” of charge, 50-30%, the battery drained overall too fast compared with what I was doing. You can see that drop in screenshot below.

Ios version it’s 15.3, also before 15.0 I have done a fresh install. What is this behavior ? It’s normal? Has happened to someone something similar ?

i have to mention that the autonomy overall is good.

Thanks and have a great day/night!