Strange issue with emails not showing up in Outlook 2011 inbox

One of my clients is having a really weird issue with Outlook on her Mac. 90% of the time she is able to connect to our exchange server (port 993) and get her email but every once in a while she will have emails that don’t show up in her inbox. She will receive them on her phone and they will show up in outlook web but they just don’t show up in her outlook 2011 inbox. What is weird is that she’ll use the search bar in outlook to search by the subject line of the email she did not get and it will show up in the search results. Once she closes out of the search results, it will show up in her regular inbox. What? Can anyone help me figure out this strange issue?

Outlook 2011 with IMAP (993)
Exchange Server 2007