First time posting- I also began following this site when Sydney Loofe went missing as that was local for me. I am the same age as her so it was terrifying and continues to be so scary. Came here to read the discussion on Mollie when a missing poster for her popped up on my Facebook a few days ago. I typically just lurk but I keep seeing the Snapchat caption thing come up (not going to quote, too many posts). I had a few things to add-
First, I have an aunt who is obsessed with SC and my cousins (who all happen to live in small town Iowa) are as well. I probably receive easily 15 snaps (videos/selfies/random photos with captions) a day from them and it gets to the point where I often click thru and don't pay much more than a one second glance at them. My aunt recently barraged me at a wedding for not snapping her enough to keep a streak or stay on her best friend's list, which is simply a list of people you snap with most often that only you can see. It is not like a Myspace top 10 or anything like that to prove a friendship or relationship status. So, given what BF's mom said re him not being into social media and them exchanging silly back and forths to move him up on her list, I would wager a guess that he was a little bit "over it" or just not paying much attention to the last snap (the pre-10 pm goodnigbt snap) that night after he got done with work.
Also, I would barely remember my last snap to my BF or anyone else, let alone what they said to me. Not suspicious to me at all (and doesn't lead me to believe he is hiding an argument) that he isn't providing word for word what she said. It is not the place where I, or anyone I know, discusses important things or argues. Most women in my age range (early 20s) would not argue over Snap, we would send texts so we could re-read and/or screenshot without our boyfriend knowing if we wanted to.

Snapchat deletes the messages after you close the conversation if you do not swipe and save the messages in the chat and alerts the other person if you screenshot anything.
Sorry for the wall of text, especially if everyone has moved on since I started typing.
I don't know what happened to Mollie, but it sounds like it could be any number of worst case scenarios I've been afraid of happening to me while alone and house and dog sitting for my own friends and family. If I was missing I would want my family to act just like hers is and keep the integrity of the investigation. I know I would also be glad to have as many people discussing my case however much they did/didn't know in a respectful way (like on this forum). Back to lurking!