I keep getting it too. This happens from time to time with various content, and in my experience, they eventually go away. Whether that's because someone uses the in-app feedback to tell them about it, or because they get around to fixing it all on their own, I don't know. IMO, unless you need that manual and can't open it, I wouldn't worry about it. (If you do need the manual, please use the in-app feedback to let them know it's urgent for you - enough of those and I imagine it will speed things up.)
But be aware that sooner or later, another bit of content will throw a similar error for a while, until it's fixed.
FWIW,
Liz