I didn’t read through the entire thread so this may have been mentioned but a few things come to mind.
1. Check the expander button and measure the I.D. Of the sized case. I like around 0.02” difference to maintain nice even neck tension.
2. Chamfer the neck.
3. Use a Lyman M die. I use these for my problem children Cast and keeps me from sizing them down by mistake
And by the way, been there, done that brother!