Long after having completed pretty much everything pertaining to The Final Shape's main story quests and all of the side quests, I have yet to find Page 5 of the Companions lore book and I do not believe I have been able to find any other sources that have listed where exactly it can be found. All I could really find is a few other players also running into the same conundrum, so I am assuming it's a bug. If so, I hope it might be on the docket for eventually being addressed, but I do still want to bring attention to it just in case it has flown under the radar.