Are we talking about the Russians? I don't think so!
Obviously, no 1 energy system is used in isolation, BUT the lifting of weights, even sets of 2-3 reps will primarily use the ATP-CP system. Unless you're completely depleting your muscle and glycogen liver stores, which isn't going to happen in 24hrs, then there must be some other factor causing a drop in performance.
I actually know a couple of people using IF at this time and they might not be lifting 6+ times a week but they are lifting 4x weekly, plus fasted sscv work on top and their performance isn't being affected in the slightest