When I do Westside my stamina goes down too. I attribute it to all the triple and single work and the fact that there is never a day that is dedicated to Max Weight for reps. Simply enough, if you dont train for reps you wont get more reps.
Your 1RM strength is important in PL meets, sure. Though, if you focus on it, it will be inevitable that you lose stamina. If you improve your stamina then you will lose 1RM strength. This is true only to a certain extent.
Hey, this is just what I noticed with me and a lot of others. There is usually a trade off. I used to be able to hit 265x8 overhead and when I started to focus on max OHP I hit 305x1 but could only get 265x6 the next week. I wouldnt really worry about it. Just about priorities.
BTW, I love the reverse band bench press! Its way better than just doing lockouts, ya know?