Different apps in background are draining battery randomly

In short: sometimes apps like instagram, spotify, telegram and iphoto are being stuck in background and causing phone heating and battery drain for like percent per minute.

Preconditions:

I've got a new iPhone 12 mini 1 month ago, it is not used, battery health is 100%, not replaced, not refurbished, just a new phone in ideal condition.

I've set up this phone using ~45GB backup from older one (iPhone X) with iOS14.7.

Right now mini is running 14.7.1.

Phone is not in some warm case or something like that, phone is being charged (mostly) once a day using Qi charger with no complains in past 3 years with any other phones.

Phone is not running under direct sunlight or heating because of something else.

What's happening: sometimes (more like once a day) with phone in locked state I'm just starting to feel that phone upper-back side is getting hot – probably cpu is running under full load. After I see that phone is hot I'm checking what is running right now, and there is nothing suspicious – regular set of apps like spotify, instagram, telegram, viber, all of them in background without any weird modes when phone is allowing them to run in background. No gps activity, cameras or whatever is can be battery-draining.

At that point I'm checking settings>battery and every time it is different apps on top with 20-40% battery usage, regular list of battery eaters is: Siri, Spotify, Telegram, Instagram. I'm killing that top app from background and after that phone is getting colder, battery stops to leak (in case of Siri there were no way to kill it from background tasks, so I've been reloading phone and disabling it in apps settings)

In settings for every app I've turned off Siri services, other background activities are allowed.

From my perspective it looks like something is broken with system's backgrounding mechanism and apps are getting stuck while trying to do their regular background tasks. I believe that all of them are trying to do some indexing in background, and were doing that for years without any issues, but right now, as far as that's not only one app, I consider that bug is on iOS side.

Probably, this issue is somehow related to the fact, that I've migratetd from phone to phone using full backup, and some old indexes/caches can cause issue, but the is no way to do full reset and re-setup phone that is being used everyday.