How to change pattern without knowing old one?

[AC Question]

So I have no idea how this happened but somehow my pattern pass changed. No one has had access to my phone other than me. I've been using my fingerprint to get into my phone and tried changing my pattern but unfortunately you need to know the old pattern to make a new one. I'm pretty sure I was using my pattern earlier today to get into my phone and it worked without problems. Does anyone have any idea how this happened? I'm sure some people would say that someone is ******* with me but I've been the only person using my phone for the last few days and only 1 other person knows my password and has their fingerprint in my phone and I haven't seen them in days. And I can't factory reset my phone without my pattern lock and now I can't turn off my phone because I won't be able to get back in since it doesn't let you use your fingerprint upon first unlock after a reset.