So I've gone laboriously through this thread and many other sites like Reddit where this issue crops up. I am utterly at a loss as to how to resolve this.
I'm using an iPhone 6s, running 11.3 (which supposedly corrected this problem from 11.2).
However: I literally cannot find Lyrics anywhere. It does NOT show up as an option when I do the whole mini-artwork-song-shows-up-in-pink-press-and-hold-on-the-song-title method described, and I updated to 11.3 when it was promptly released and it resolved nothing. Still no "Lyrics" showing up anywhere in my system. And yes, these are songs that have "Custom Lyrics" checked and lyrics populated for them on my desktop and laptop copies of iTunes. And yes, I am a signed-up user of the Apple Store with a working Apple ID and everything.
I think flat-out it's just stupidity on Apple's part at this point. Laziness in quality control. Other people talk about having to completely re-install their libraries and so forth and nobody should have to go through that just to have a feature that worked perfectly fine on older devices and OSes.
Why does this have to be so artificially complicated? Why not simply let us have lyrics for a song, and a lyrics button that is ALWAYS there right in the song-expanded view window, and it's greyed out if there are no lyrics but if you have them then you just click. No hunting around or guesswork or complete change of where it's hidden with every new release. Apple used to pride itself on consistency in its design philosophy and logic and intuitive ease-of-end-user experience. Did all that really die with Steve? Beginning to think so.
Tonight I'm downloading 11.4. So let's see if MAYBE Apple can fix something that wasn't broke in the first place until they 'upgraded' it.