Guest mode welcome message not allowed

I have over 40 Roku TVs set up at vacation rental properties that I manage. I customize the welcome message to the house name, and have never had any issues until now. The website is rejecting "Welcome to Island Stones!" with the error message stating that this "doesn't meet the requirements."

I've narrowed it down to the word "Stones" as the problem, but WHY? What could Roku possibly have against that word? Very weird.