Never buy a OnePlus phone ever again. They now have a hardware anti-rollback fuse that blows if you revert to an earlier version or install a custom ROM.

https://consumerrights.wiki/w/Oneplus_phone_update_introduces_hardware_anti-rollback

Oneplus phone update introduces hardware anti-rollback

Consumer Rights Wiki
@davidgerard Man, my OnePlus 3 was one of the best phones I owned. What a shame.
@derrickb @davidgerard my 3T was great and lasted many years. But that was back when they still remembered they needed customers to want their hardware.