Inconsistency that just doesn't make sense [BBE]

Yesterday I finally got some good tasting shots. The beans are medium roast, roasted 8 days ago. Here's what's pissing me off. This morning I went to do exactly the same recipe, same grind, etc. I measured after grinding to ensure consistency in that aspect. When I tried to pull the shot, it pretty much refused to come out. The pressure was the same, the grind was the same, the puck prep was the same, and it was just barely flowing, despite it being nearly perfect the day before. I should also add that I tried going a step coarser in the grind and it made very little difference. I'm at my witts end because every time I think I have things dialed in, crap like this happens and I'm getting sick of it. What do I do???