I recently upgraded my Nexus 5x to a pixel 2. I use Media Monkey to send music and music videos to my phone. However, I have a decent chunk of seemingly random albums where Poweramp is saying unknown artist and album. The files are properly read in other music apps. They were also placed in the proper folder on my phone by Media Monkey based on artist and album. These files had no problem on my Nexus 5x.
I am on v2 build 588-play.
I'd offer to send a sample mp3 but they are copyrighted, so not sure if that's ok.