I can confirm findings posted above as well and would like to share my observations.
From a first look the issues seems to be related to a service(s) or daemon(s) that got "stuck" when using 5G wifi network or most likely when network is reset.
I've tested with 4 different routers consumer grade netgears (R7000,R9000) , AT&T uverse, and enterprise grade HP Aruba with 3 Apple devices iPhone 6, 6s and 5th gen iPad and results are with respect to power consumption are consistent it goes up when using 5g wifi network. The impact varies between devices .. from ~2x times for iPad to ~20x times for iphone6, but doesn't depend on router I'm using.
Iphone 6s was reset to factory defaults to have a reference point and make sure it's not due some app that I have.
All devices were fully charged and rebooted before each test. Each test was 12h or until battery drops below 80% whatever comes first all background services/activities were disabled.
When device is connected to 5G network, I see that after some time (typically 10-60 mins) device drops from network and reconnects. This never happens with 2.4G networks. Until connection is dropped for the first time the power consumption seems to be the same for 2.4 and 5G networks in averaged ~0.5% per hour for iPhones (~0.1% iPad)
After first network drop on 5G wifi power consumption goes up. Worst was iphone6 which in average consumes ~10% per hour while idling (screen off)
Once 5g-network-drop happens, switching between networks (I.E going to 2.4G), turning on/of Wifi or Airplane mode, doesn't help, but reset does help.
On iPhone 6 after initial "drop", some services become unavailable, for example phone can no longer see Airplay enabled Yamaha received, or stream audio over BT to my Car (in the same time calls over BT works fine). This never happens if all 5G networks are disabled and phone is allowed to connect to 2.4G networks only.
In my personal opinion there's some issue with network services and/or driver which cause a network to be reset. Depending on device it may or may not fully recover, older (slower) devices are more prone to the issue and often not all servers are properly function after network is reconnected so most likely there's some race condition in one of the services as well. This can also explain why different app can start to consume too much battery. Whatever app was last to access service that stuck, goes to the top of battery consumption chart.
After running tests I downloaded logs but I don't see any (new) crashes.
nsurlsessiond process shows a bit high cpuTime, but I have no knowledge about iOS so don't know if it's the one to blame or just another victim.
I've submitted ticket to Apple they run all diagnostics/collected logs as well, but so far found no smoking gun. They promised to send it to engineering, will see how it goes.
Hope that helps.
