Hi Brendan,
I'd like to confirm you are using your Office 365 email account on Outlook for Mac. Does the issue persist if you are using other applications on your Mac?
Actually, as you said, you can scroll through your conversation list with the mouse and trackpad on your Chromebook, so the issue is more likely to be related to your Outlook client on OS X. Since our forum mainly focuses on Office 365 Online services, it is recommended that you contact the specialist Outlook for Mac Forum for effective support. Thanks for your understanding.
Best Regards,
Alex