Squibs
Lots of squibs.
I started shooting some fmj .38 special I loaded a few years ago and have already had 5-6 squibs.
Before this batch I've had one squib since I was 14 that was was from me loading.
I think what happened was that I got to the bottom of the canister before I realized and wasn't checking every case.
Where I loaded in my basement at my last house in Rhode Island the lighting wasn't great. That's the only thing I can think of.
I'm going to shoot the rest as slow fire only.