My theory of the LinkedIn "creepy" message is that Missy may have been using LinkedIN to have a "flirtatious" (I will be charitable) conversation with CW. Then, for whatever reason forgot and left it open with some message from CW still on the screen and then the phone timed out. At some point, perhaps at a friends house, she might have been asked if she had any pictures from Austin, for example, and Missy went to show that and whoops! there was a CW message. I would think that Missy would have closed it quickly and then acted surprised and denied knowing what that was or knowing who that was. MPD was asked about that and they said they hadn't been able to track it down - this is why I think it was a message from CW.
An observation I will make about the use of LinkedIN. When people are running around they often use various apps that encrypt or hide things or are disguised apps for communication, etc. The very presence of such things would be a good bet that something is going on. The clever cheaters, most especially the ones that aren't on their first rodeo (especially having been caught before) will use other means. LinkedIN might be one. A website that has chat available, especially private chat, that is for some other purpose like being all about a specific TV show, for example, might be used. Or say a Crime oriented site with private messaging. Or a cooking/recipe site. Any site really that would be something that you wouldn't expect. Obviously, having things like multiple FB accounts, Twitter (for private Direct Messages), etc. are also used but the person using them either starts them in a private browser window or never saves the login information - this is same thing is often seen with e-mail accounts where the account information is saved. There are ways of uncovering such shenanigans but I won't get into how that might be done and things change quickly so it is always a moving target to know what is current "soup of the day" in cheaterland - or criminal land for that matter.