I had a similar experience recently with Fiocchi small pistol primers, mild load of True Blue (5.0 gr) and S&B brass. I have loaded 100’s of 9mm and .357 Mag with these primers previously without issue, but these were too light to function in a Glock 19 or CZ P-09. Perhaps it was a combination of colder weather (50 degrees) and lighter powder charge (Sierra No.6 max!), but I was quite surprised. In checking older Western Powder suggested starting loads, I was at least .5 of a grain under their suggested weight for True Blue and 115 gr bullets. I replaced the new factory recoil spring in my Glock 19 with the original old one (hoping it is tired after over 20 years and thousands of rounds) to see if it can run them. I may wait until summer and 100 degree temperatures to give them another try. I should have tested them with a smaller batch before I loaded 200 of them..