Spent 10 years as an installer in the central valley and the two biggest problems I always encountered was the flue was less than 2 feet higher than anything within 10 feet .I see a tree in one photo and you are on the backside of the roof from the wind. those two items create a lot of down pressure to the flue .Raie the flue above that 2 and 10 rule and add a directional cap.
