@Gentle-Ent Hi, I haven't been around here for some time and it's a bit late now in september, but if you're still looking for a solution, I've had a similar experience with an OPO a few months ago and this helped me out:
https://forum.xda-developers.com/oneplus-one/general/guide-return-opo-to-100-stock-t2826541

After having restored this factory image on the phone I was able to install UT succesfully with the snap version of the Ubports installer.