Okay buckle up.
After major cutscenes, I’ve found particularly with main story line quest involving Sigurd but not exclusively the screen becomes becomes various shades of light gray like an over exposed screen. The only other time I’ve ever seen the is when coming out off some of the flying agaric missions and the first time it happened was after meeting Ceowulf for the first time when that cut scene ended and you’re outside the longhouse with Sigurd and Basim. Reloaded the game and lost 2hrs of game play. The only way I have been able to fix this is by interacting with some sort of NPC shopkeeper. Today the game started strobing vivid unnatural colours around objects while I was killing the Zealot near Cordelia. I fast travelled back to my village and interacted with my now go to shopkeeper the blacksmith to fix it and the strobing stop but the game lost all sound as I was going to hand in my medallions. Exited to the Home Screen and came back without shutting down just to confirm it was the game and it was. Decided to reload the game and came back to not just the find once again the over exposed gray screen but that I had lost an hr of game play as someone that has clocked up over 70hrs of game play and was only just getting into the Cent storyline now you may be able to tell I like grinding and so I just lost the start of the Cent story, three Zealot Kills, at least 2 mystery, some artefacts and entire towns cleared of any loot in lower Cent on my way to Dover. Just the general gameplay is glitched to eg. Floating boats in Vinland, can’t see other player photos, I unsuccessfully tried to dodge a reindeer kick the other day and ended stuck half in the ground still trying to dodge. It been a crappy yr as it is and I think this might me putting down the controller on this franchise for good.


*Possible spoilers I don’t know how far along you are*
Also just some feedback Sigurd is the mostly poorly written character I’ve come across. I have no desire to interact him, I avoid missions involving him for as long as possible and am intentionally go out of my way to get the “bad ending” so he goes away. Frankly I wish there was an ending where he died I wouldn’t feel so guilty about the interaction options I have with Randvi. There no bonding with that character, he’s just shows up and is like “your my brother” and after all the social distancing I’ve done this year I’m going to need abit more then that. He’s also gone for major chunks of the other story lines. I have alliances with more then half the map (5-6 regions) and he was only there for Mercia. I can’t resist a good spoiler and the plot for this is game is flimsy at best and it’s highly offensive that this is franchises best selling game on release when Ubisoft has put out something with more issues then AC Unity. Personally I’ve lost probably a total of 8+ he in the three times now I’ve lost data and I still haven’t been able to download the berserker pack from the code that I got with my game. The season pass with barely any content on though works just fine. I wish I could just get my money back and pretend like it didn’t exist. I own every single AC game released on Xbox and I’m embarrassed to have this in my collection.

I might be wrong, but I think the gray strobe effect you described is due to being poisoned in some mystery event. I read that you have to kill the bard that poisoned you to stop it.

(I'll look for it and see if I can find it for you because I don't remember what or where that mystery event is)

*spoiler*
I don't think we can do anything about Sigurd : /

Finally....

https://discussions.ubisoft.com/topic/80230/bug-loading-save-after-death-makes-screen-grey-and-monotone-like-walking-in-a-black-and-white-movie?_=1606236870439

Hope this is your issue and it solves it for you.