Series X is doing background updates, etc while fully powered off in “energy savings” mode.

xbox one is constantly updating your friends and feeds and so on , but it should not be doing it in energy-saving mode , it should be ALL the way off , that's why it takes so long to boot up in that mode...maybe yours isn't in that mode or it isn't working
properly...

Energy-saving power mode

In energy-saving power mode, your console is shut down to save energy. In this mode:

•Updates are not downloaded and installed until your console is turned on.

•Your console takes 45 seconds to start up.

•You must press the Xbox button to start the console.

Notes

•In energy-saving mode, the PSU is in off/standby mode and the solid orange LED on the PSU is bright.

•The console uses 0.5 watts of power when in energy-saving mode.

so if the psu is off , I don't see how it could use the internet...

go to SETTINGS on CONSOLE, then POWER SETTINGS, and change the power mode on console to ENERGY SAVING MODE, now when you turn off console , it will turn off hard drive, and turns off fan on power supply. It will no download updated while off.

Yes my ups has a battery and it there for the uninterrupted power but when i turn off the ups, it cuts off power from everything that's connected to it.

Also I've unplugged the xbox before and still after plugging in and powering on after couple of hours it still turns on instantly without going into cold boot.

And just now i was checking the energy save mode and found that the console doesn't just fully turn off if energy saving mode is on. It takes about 5minutes to turn off fully.

So for me i think standby is fine and i can just fully shutdown console before removing power if removing power while on standby is actually hurting the xbox.

Honestly instant on screws a lot of things up, in the long run its far better to have your One set to energy saving mode, it only takes like 10-15 seconds to turn on but it clears the cache each times, prevents a lot of network issues and the external drive
powers off fully. You wont have background downloads and updates though.

Set your xbox one's power mode to energy saving instead of the default instant on and it will allow the system to fully shut down when you turn off the system instead of staying in a standby based off state. This will let the ram boot up clean and wont
have this issue. You can reenable instant on mode once you reboot with energy saving mode. But ive found it best to atleast turn off ur xbox with energy saving on atleast once a week to let it do a full startup.