Since I have had the problem with highlights, as far as I can remember, ever since I bought the Kobo, I tried with a book coming from our "local" library, thus accessible to anyone. I just started to flip pages and make a highlight or two on each page.
This is highlight number 11:
(All 10 first highlights worked fine, even those starting with a space.)
I assume the book should be ok, regarding formatting/code.
J.S. Fletcher - The Middle Temple Murder
https://www.mobileread.com/forums/showthread.php?t=29405
If you still think it would be helpful to look at the book I was reading, I'm happy to send it to you via pm.