[Q] How to install CM12 on 10c? topic

So I have a T-Mobile LG G3 (d851) with a rooted 10c and TWRP.
I flashed the latest CM12.1 but when I boot into CM12 I am unable to hang up calls. If I make a call and tap the red "hang up" button the dialer says "Hanging up" but never does and I continue to hear the other party.

I am sure this has something to do with the 10c radio on Lollipop but maybe not.

I found flashable zips for the 20b radio and successfully upgraded it but that didn't solve the problem with disconnecting a call. I am at a loss here, especially since when I check for an OTA via the phone's UI I get the "you have the latest software" message.

Anyone have any ideas?