Had to go back to PA 7.3.1. Eye strain and headaches forced me to downgrade.
Installing Paranoid Android on OnePlus 3
Tried some new ROM. No good.
Tried to flash PA again after using MSMDownloadTool.
Getting the Wifi not working problem again. Very frustrating.
I found this today:
https://github.com/AOSPA/android_device_oneplus_oneplus3
I'm just leaving this here, in case anyone is ever interested in finding out what exactly changed that the OnePlus3 became uncomfortable to use on later Paranoid Android releases.
It seems this website contains the complete history of changes for different Android versions. The selected one by default is "quartz". You can see already that a lot has changed regarding color spaces (which might be the cause of the eye strain, as discussed in other threads). Older Android versions can also be selected. Paranoid Android 7.3.1 must be one of the "nougat" branches.
I'm currently happy that I can use my device with the old OS, so currently I'm not interested in changing anything. However, if one were to investigate how to modify the new code to have the old "nougat" (Paranoid Android 7.3.1) color space/profile behavior and how to build a functioning ROM, perhaps the mystery could one day be revealed.