Can you file for divorce, have the finalized papers from it and turn out something is finalized “wrong” years later?

Little backstory, my boyfriend and I started dating around two years ago. He’s been divorced since 2013 and around August of this year, his ex wife texted him saying that they have to redo the papers because something wasn’t finalized right. So does this mean they are technically still married? We are kind of confused because we keep asking her to update us about them or explain to us what happened (we recently got engaged) and she keeps saying that she keeps messing up or something like “I haven’t got the chance to do them yet” or “I’ll handle it don’t worry”

It’s just weird to me.