Every Kobo reader is capable of running KoReader ( http://koreader.rocks/ ). That's the first, and probably last, step I'd take to render a book that the default reader takes issue with.
Ebook producers really should be forced to either drop drm or adopt a cross-platform standard.
The publishing industry never got its head out of... some dark place. We've been able to buy mp3s without drm for ages, but somehow books are different.
KoReader also gave me a lot of freedom to manage the bad battery life of my Kobo Sage before it died of other causes. Definitely worth the extra cognitive load of dealing with the two experiences.