Its Just the System. So it Shows me in the settings. I have the same problem with LineageOS. I use the latest TWRP and wipe everything exepct recovery, Boot and otg usb. (I don't know what otg usb mean, so i don't wipe)
It's wierd, try to
1. flash stock rom android 6 with sp flash tool
2. Look if you have Always tour IMEI if not send me mp
3. Flash twrp
4. Flash aokp ans gapp