Why are my purple hull pea pods drying on the vine before they mature and turn purple?

Question

My purple hull pea plants voluntarily grew from the remnants of last year’s crop.

Answer 1

Weather conditions; excess heat or uneven watering could cause issues.
Also these can cross pollinate so you could have a different type of pea growing from this self seeded variety.

https://www.gardeningknowhow.com/edible/vegetables/beans/how-to-grow-purple-hull-peas.htm