I want to share my experience in case it helps anyone else.
While dealing with a potential virus this morning, I made some changes to Windows settings and hunted through my registry to ensure it was dead. Afterward I launched PSO2 and encountered repeated NP1002 and NP0 errors. Research told me these were GameGuard related but none of the suggestions I found online helped.
I discovered the problem myself. It turns out the memory-based protection in Windows Defender, which I had arbitrarily enabled in my virus hunt, stops GameGuard from being able to interact with PSO2. To turn this feature off, try:
Windows Defender > Device Security > Core Isolation, and tick the box off.
This solved my problem immediately. If anyone else has this specific issue, I hope this post helps you.