Don't shoot it!
When the bullets are press back down into the case as you said, not enough crimp was used and its dangerous to fire them.
An increase in pressure.
As they hit the ramp going into the barrel, not enough force was exerted crimping the bullet to the caseand this causes the push back.
If these are doing that, the ones you tested, the remainer of the box/lot will do it as well as you shoot them.
If you've ever seen an old ARMY issue .45 ACP round, many had a SEVERE crimp at the point where the bullet was seated into the case.
This was to prevent what you have happening with the .380.
I hope these were reloads, factory normally does NOT have this issue.
You may find me dead in a ditch one day, but I will be up to my waist in spent rifle brass!