Hi @mb11 Welcome to the forum! 
Outlook recently changed their default paste behavior to Match Destination Formatting instead of Keep Source Formatting. This is breaking the insertion of snippets containing styles like highlights.
We have steps available for how to resolve this on Windows (Bug with inserting tables via extension vs desktop app? - #5 by Ashwin_MittalTB). Sadly I'm not able to find the steps for Outlook on Mac.
We will look into and get back to you asap.
Best,
Gaurang