I have checked the lenses, aperture blades and the lens body itself again and couldn't find anything.
Then I did some more test photos and found some interesting outcome.
Shouting from INSIDE the building into outside didn't gave me a fog at all.
Shouting OUTSIDE and the fog was back again. Then I tried a longer lens hood - no effect. Even with almost 5" lens hood the flare/fog was still there and still at the same level.
Both pictures taken at f1:22
INSIDE to outside picture:
Outside picture:
Both at f1:22