Heat waves can cause cannabis plants leaves to yellow and dry out indoors and outdoors. Temperatures above 28°C prevent cannabis plants from efficiently photosynthesising and cause buds to form more loosely and airy.
I don't think the yellows will ever be the same again, hopefully conditions improve, as long as you are sure PH and nutes have been all good I expect you are right.
But the temperature at my canopy is similar and green and pleasant land.
Who knows