Nuva ring hormone tolerance?

Hello everyone! I’ve been googling but I can’t find any answers! I’m 18 and I’ve been on the nuva ring for about two years and I just noticed some spotting. This never happens unless very close to my period dates. I’m in the middle of a cycle so it has me worried. Has anyone built up a tolerance to the ring and has gotten pregnant? Im just trying to see if I should be worried about my protection or if I’ve built up a tolerance to it. Has this happened to anyone else? I’m gonna call my OB and all that but if anyone has experienced anything similar please let me know!