I guess I missed the part where you said that 2 of 4 bines basically died ("stopped growing"). It's probably too late for them to do much more this year, but next year I bet they'll come back just fine, especially if you fertilize and mulch.
Funny... I recently read the same sort of thing about potassium deficiency, and as a matter of fact, I wasn't sure about my own plants having yellow leaves so I already bought some high K fertilizer and dumped it on last week. I guess great minds think alike, or find the same information, or something.
But lucky for me, my plants are still alive and well, currently about 17 feet high and FINALLY beginning to flower. Both my plants flowered awfully late this year. I think it has something to do with the enormous amount of rainfall this year. Hop plants seem to NEED to dry out a bit, basically dying at the tips, before they'll even begin to think about flowering. But my Cascade tips are STILL growing. It's crazy. My Hallertauers have looped the loop so many times at the top of my trellises that there's no doubt that they are probably a good 25 feet tall if I could stretch them out. But anyway... I digress......
I wish you, and all the hop growers out there, the best of luck this year.