"Sounds" like the beginning of a nutrient issue, namely potassium, which is hard to diagnose.
Hop Disease and Pest Symptoms
The problem with nutrient issues is that "too much" looks the same as "too little" and also that overwatering, be it natural or irrigated, has the same appearance. Another fun one is that some of the micro-nutrient deficiencies combined can appear similar to a macro-nutrient deficiency.
Starts to make sense why (some of) the bigger yards spend so much on detailed soils testing and custom blended fertilizers.
Ain't hop growin' Fuuuuuuuun?