wi-fi + bluetooth + usb failed for no reason (no system update) on xiaomi redmi note 4 Some time ago I suddenly noted that wi-fi switch does not turn on wi-fi and I could not start wi-fi hotspot on xiaomi redmi note 4. I did not do any system update before that happened.
As I've read on that problem on internet reset do not help, and neither it helped me later on. (installing some pdanet app did not help either).

In addition to wi-fi, also bluetooth starts (icon shows it's on, not like wi-fi always off), but does not find any devices.

I wanted to debug from PC, but neither Windows nor Linux see the phone connected as device, only charging worked. I was surprised to find out that OTG works, that points to software root cause IMHO.

The phone has non-removable battery, I cannot easily try what I've read as second advice (for samsung with wifi issue) - take out battery.

What could be the issue and what else do you advice me to try apart from selling for spare parts?
This seems like a technical issue. There could be these possible reasons:


It can happen if you manually change radio settings of the device (but will auto reset to default when you boot the device).
It can happen if you are running your device with an outdated version of custom UI that is not installing OTA updates.


OTA Definition:


  OTA Updates - Android devices gets OTA updates via developer provided directly to your phone under name 'software update' or 'system update' or in some devices directly through app named 'Updater'.


Solution is:


Try factory reset to your device.

Factory resetting to your device makes the device completely clean and settings will revert to the manufacturer default settings.
Try manually updating the ROM.

OTA update is an automatic process for keeping your mobile up-to-date while manually updating a ROM takes time and a little knowledge of android devices.


Benefit is - By manual updating you can get a custom ROM installed faster than others who are waiting for official OTA update that takes time.

Caution -Manual update can be a risky process for your device. Please search it well before trying manual process.