I have a problem with Lineage OS unofficial ROM on Xperia Z3 Compact Tablet from this xda thread.
When mobile connection (using SIM card) is established, Android overwrites allowed Wifi channels settings with restrictions, based on countries. This is a well known feature, but for Russia it seems that any 5Ghz channel becomes restricted - even through channnels 34-165 are legally allowed in Russia (I can't see any networks, no matter what channel I use on my access point).
I want to find, where those restrictions are located, and fix them with appropriate values (I suppose there should be some kind of table with those values). I am sure that this is possible because 5Ghz works both on this device with official ROM and on xiaomi device with official and Lineage OS ROMs.
Unfortunately, ROM author is not interested in fixing this bug so I want to do it myself. I managed to get 5Ghz working using Magisk, Xposed Framework and module for fixing region - but that solution is damn unstable to I want to avoid it and make a normal fix.
By the way, setWifiCountryCodeFromMcc is met in this source and it calls "setCountryCode" from here. I just need to go a little bit deeper to find restricted channel options - but I don't know where and how.