I seem to have that same condition at times on some plants and have been attributing it to uneven irrigation. It looks like drought stress as talked about in this University of Michigan page.
I’ve improved my chlorosis issues by adding sulfuric acid to irrigation water.. The study mentions this a common practice but I don’t understand why they didn’t include it in one of their samples. They raise concerns that this method could hurt the soil microbe with nothing to back it up. Hope they are wrong!
I use rainwater for gravity-fed irrigation and having enough capacity is always an issue. I don’t want to use this resource on growing grass when a squirt of battery acid can more efficiently do the job. I’m still tempted to try adding some red fescue to one of a pair that still show signs of chlorosis.