First off, we're going to start by correcting your headline, because it ***is*** a hardware problem. Here's the smoking gun.
[quote|format=featured]SD: 1 BC: 1 RC: -1 BS: 2, Missing sensor(s): mic2[/quote]
My esteemed colleague @flannelist has written iFixit's authoritative [[iPhone Kernel Panics|guide to Kernel Panics|new_window=true]] and it points you straight to the problem. Here's the relevant part.
[quote|format=featured]* ***Mic2*** is in the [link|https://www.ifixit.com/Parts/iPhone/Cables?q=power%20button|power button flex|new_window=true] in most models.[/quote]
So even though you've changed the power button flex, you're still having the problem. So there are two possibilities; either your replacement flex is defective and either doesn't support or has a bad sensor, or else there's a problem with the communication channel on the logic board. In the latter case you'll be looking for perhaps a damaged pin on the motherboard connector or maybe a component next to the connector got knocked off in the process of working on the phone.
My suggestion would be to just bite the bullet and get another power flex and swap it out. They're not expensive and that will help pinpoint the problem. While you're in the process of changing it, you can check the connector and the logic board and see what happens.