I can't think of anything. I have multiple different types of proof of meeting in the last 2 years (still in the time frame as of today), two separate letters of intent to marry, passport pictures, all required forms, etc. Nothing complicated about my application either (no divorce, no criminal history, etc). I'm just hoping it's something really small and simple.
I feel like most current people stop posting updates once they get RFEs so we never know what random reasons to expect. I'm surprised we rarely get posts for such high RFE rates in the lat few months. I'll for sure keep you updated on what they asked for.