I have switched lots of H4350 with all other components identical with identical powder charge and blew primers. Had to pull the other bullets. I now back off and work up every time I change powder lots.
I've had the same experience. I now try to buy H4350 at least 16lbs at a time (2 8lb in the same lot).
The velocity change you got while dropping 1 grain of powder is pretty normal. I just cracked the seal on a new 8 lb jug of H4831SC and had to add 2 grains to get back the lost velocity. I canít think of a lot change Iíve made where there wasnít a change in burn rate.
A 30-06 packs a slug of powder behind the bullets, which isn't burned at all in a short barrel until released at the muzzle.
This contributes to increased recoil, ES, reduced accuracy(compared to better designs), and as you found, adding more powder beyond burn reduces velocity -with a 30-06(not with most cartridges).
All I can say is WOW. I usually buy rl in 5# bottles, but I've been buying rl25 in #ers lately as the 5# jugs are higher per pound. I haven't noticed a bit of difference even with stuff that was packaged a couple of years apart. I don't buy enough H to know any better I guess, though it seems when I do buy it I'll but a 8#keg (to keep from getting ripped off locally) so I don't really have multiple lots to deal with.