When you lube a case, don't put lube on the shoulder. You can put just a little on the neck, and some on the base and middle of the case, and twirl it in your fingers to get it evenly distributed. I even take a piece of paper towel or shop rag, and wipe the shoulder to make sure no lube is on it before sizing. Also, make sure the vent hole in the die is not clogged. If it is, you can get a dent in the side or shoulder of the case. Just use a straight pin or needle to make sure the hole is clear.
The dent in the shoulder, although unsightly, won't cause any problems and will come out when you fire that round in the gun.
If I am sizing a case, and it seems to be really tight, I back it out a little, and put a dab of lube on my fingers and rub it on the case. I then turn the case about 180 degrees in the shell holder and try again to resize it.