Hey Caitlyn,
Sorry to hear about your difficulties. Adding the highlight within the text worked fine for me. Would you mind sharing with us the screenshot of the error message? Also, is this happening for every project or specific ones? Could you please try adding highlight text on a different project?
You might also want to try working after clearing the cache and cookies of the browsers or on the incognito browser mode. Let us know how this goes.
Thanks for your patience.
Regards,
Amitej