Check the bullets ,I got a box of bullets a few years back that were slightly undersized.
When you expand ,only expand enough to just sit the bullet in the flare.
Is the taper crimp die pushing the brass up against the bullet ?
Are the dies new ? Steel or carbide ?
I have a old steel 45 acp sizer that is worn out ( over sized ) due to lack of sizing lube.
You may need to replace the sizing die.