I have tried searching for a topic about this, but it does not seem to be mentioned anywhere, but for some reason in the AoS app the Old Blood on Carnos Sunstone spear is listed as 1d3 damage, while the book says 3 damage. With no errata or faq stating anything else, I assume the book is what counts, but it is just odd and makes me wonder if GW has just missed this entirely, and what is really intended.
It is a flat 3 damage. There are currently a number of mistakes for Seraphon in the AoS app, and it hasn't been updated in months.
If ever you come across a discrepancy like this there WONT be a FAQ if the book is right. order of precedence, and always by most recent release date is FAQ/Designer commentary, book, then app. app is just a quick reference.
ALWAYS USE THE BOOK ALWAYS. the apps are junk and often have glitches and aren't always up to date. the only thing that over rides the book is the FAQ