Our Sales team had found the Marketo Sales Insight Outlook plugin to be pretty buggy, which has caused the MSI adoption rates to be low. It mysteriously stops working, which requires multiple re-installs, and our Sales team just gives up on the tool.
Hi Ashley- What version of Outlook does your team use? Do they also use other Outlook plugins (like SFDC)? I know that we had some folks have issues with multiple plugins loaded in Outlook - and when we were migrating from Office 2010/13 to Office 365, we had some issues there as well.
I would suggest logging a case to have Support review your issues with it.