Check for bullet squeeze.356, I want to say but I have a new batch to size and I might go .357. What I think is the problem might be slightly oversized bullets and some of the hi tek is coming off during sizing on a few. Small hiccup no biggy. Coating a bunch of .357 about 15 pounds give or take.
Grab a couple of cases with the same head stamp.
Load one normally and use a micrometer to measure diameter at the end of the case.
Slice the end off the other case cut and carefully flatten the brass to measure the case wall thickness
If measured cartridge diameter is less than 2x wall + sized diameter then you need a new expander.
If you are squeezing the base of your bullets, leading is a given