Update: I just heard from Tier 2. Once they finally confirmed that they understood my issue, they proceeded to try to tell me that they thought it was a software incompatibility between Word 2016 and my client's SharePoint.
I pointed out that my client uses Office 365 and is using their own person SharePoint directory.
Nonetheless, the Tier 2 agent was only grasping at straws and did not have any technical replies or steps for me. I thought for sure that this was logged in their system, as earlier posts here state that this issue is a "Microsoft Office for Mac, that has been reported as early as December 2013.
Anyhow, with some urging, the agent is escalating to the Engineering department. Thanks, I guess, but now have to wait for any updates, I suppose.