Hello, sorry for the delay in responding.
I visited some forums and followed some advice, I deleted the updates, clear the cache of the Xbox and reinstalled only the latest patch.
I could complete the challenges but I'm still unable to complete a side quest (more precisely one that involves a bird) The error, as I gather, came to not immediately complete this side quest ,talk to another character who gave me another quest and complete it. Taking up the first quest, though it appears initiated on the map, there is no way to locate the bird in question, as it has disappeared from the scene. Still, I decided to continue the adventure, because it seemed a waste of time to resume everything from scratch. I will not finish the game with 100% complete, but it will be 99.9%
Therefore I recommend: - Before continuing with the story, complete side quests immediately after speaking with the mission giver. - Do not talk to another mission giver, until you have completed the active side quest.
Surely another patch will appear at some point and I can try to end the slope side quest. I hope I have helped a player to avoid this inconvenience. Cheers,