Weird but I opened it up and under the A4 chip shielding there was a little bit of corrosion and it looked a bit burned on the shiled itself. There is a smallish inductor there with six gold pads, a few of those were tarnished and a little black.
I also noticed there was a tiny bit of gunk/fluff on the small white 6 pin thing near the wifi antenna contact so I cleaned that off.
I thought that was the end of it as I had no idea what to do next.
So I put it all back together and.. wifi now works fine!
No idea what happened but I guess whoever took it apart before messed something up.