I've been using IMR4756 for cast bullets for a long time, though I don't shoot anywhere as much as some of you. Today I was using 9 grains behind a 175g pb bullet trying to settle on an accuracy load. I had two FTFs in a row. First I've ever had in 50+ years of shooting.
I pulled one of the bullets and checked the powder. It looked just as it had when I measured it. So I pulled the other bullet and moved the powder to a couple of primed cases and seated new bullets.
By the time I got ready to shoot those, I was thinking maybe I didn't elevate the muzzle before taking aim. So I did this time, and both shells fired normally.
Just another example that some loads are position sensitive.