The tangled shore lore book is still bugged. Many players (myself included) have reported repeatedly on reddit and here through last season and this season that after completing the Forsaken campaign the "rifleman wanted bounty" triumph did not proc nor did 1 entry from the lore book, thus assuming the missing lore entry is associated with the rifleman quest. Subsequent completion of the heroic adventure and/or daily heroic only completes the Wanted triumph but no granting of lore entry. Some users have reported that replaying the campaign on another character does not fix this issue either. At currently, there's no official mention from bungie that this issue is being investigated and the acquisition of the Chronicler Title Seal is officially put on hold as there's no other way of obtain this entry. According to other website, the missing piece is titled : By Thy Tongue be Damned.