When it happened to me, for I used to put both phone and compass together in the lid pocket of my daysack, the needle pointed about 20 degrees west of north when compared with the replacement I had to buy.
I could tell the old one was faulty during my walk because there were distinct landmarks around me and I could see the hill whose base I was aiming for, but my compass was pointing me to one side of it.
I don't think there is a way to delete a post. On the rare occasions I've needed to, I just deleted the text and wrote two or three words to say so.