I wouldn't worry that you had a week without linear progress in one or more of your lifts. That's totally normal. You're actually throwing around some pretty good high-intermediate-level weights there, so you're unlikely to hit
PR's every workout, no matter how good the program is (and Strength I is very, very good!). You've also got a stressful schedule going there and that alone is enough to curb gains. Workout frequency is also relatively low and perhaps you've adjusted to the 2x/week schedule and need to up it a bit.
I'd say it's a combinaiton of the usual suspects: consistent diet, regular sleep, curb stress. What an insight, eh? Good luck. DF