ginacc the only reason (i think) local lyrics won’t show is because the name and artist doesn’t match. This has to be exact and even down to where there are capital letters. Sometimes even when I can see both do match it’s because one has a space at end which you can’t see so the best thing is to delete the name of the song or artist and type it out again.
It’s hard to say if this is your issue as you’d need to post screen shots from both iPads but I hope that helps solve it for you.
Although I’m not sure why changing the lyrics on one of the songs has stopped it working on that particular song mind.