Hi Matt!
Thank you for reaching out and sharing your project files! That made testing easy!
I am seeing the same behavior with your PowrPoint files when importing them into a Storyline 360 course. It is hard to tell what is causing the yellow highlight, however, I created a new PowerPoint file with the Aptos font and the highlight didn't appear when importing the new file into Storyline 360.
Is it possible to copy the text and paste it in a new PowerPoint file? Then, I would import that new file into Storyline 360.
Lastly, if you have OneDrive running, I'd pause the sync while working on the project because this issue could be related to the course having multiple versions.