Are you eating and or supplementing with magnesium? Most people, do not consume enough dietary magnesium. A slight dip below required amounts, definitely impacts strength training.
Bonus, Mg maintains good mood, good sleep and, good poops.
I also lifted heavy while fasted. My key was to hydrate well before lifting. water/vinegar mix with ice did the trick. since apple cider vinegar tastes like feet, I started making my own kimbucha vinegar….the small caffeine bump doesn’t hurt.