The statement you wrote shows that you don’t understand the seating die and how it works. Please re-read what I and others have written about adjusting the seating die. It is designed to seat the bullet and optionally crimp the case mouth. YOUR SEATING DIE IS NOT ADJUSTED PROPERLY! It needs to be unscrewed a couple turns.
The sizing die is probably just fixing the problem you created with an improperly adjusted seating die. We can talk if this is confusing. Send me a PM with your phone number and I will call you.
Here is a video from Hornady that shows the process of setting up a seating die without crimping the round:
https://m.youtube.com/watch?v=4l5qM6...fauxfullscreen
If you want to remove the case bell or add some crimp, simply screw the die in 1/4 turn and see what the result is. You may do this a couple times. Make sure you have unscrewed the seating stem so that the bullet is not being pushed deeper in the case.
Were the loads accurate? Any leading in the barrel?