Do your shells drop freely into the chamber and is the rim making full contact all around the case? I am thinking it could be the shell since you already switched primers and guns: The .410 can be tricky to load. Over crimping can bulge the case or the top near the crimp. The shell appears to chamber fine but is actually not fully seated. Firing pin strike can finish driving the shell forward into the chamber without the oomph necessary to light off the primer. It can also cause the primer to strike off center causing a FTF.
Like yourself, I have loaded thousands of 12 and 20 without a problem. I can't tell you how many .410 I screwed up trying to get the crimp right....I sorted by type and markings and still occasionally run into a crimp issue. If they weren't so @!#$ expensive I would be tempted to stick with store bought.
I use Win, CCI, Federal. Have a box on Rem to try but never had a primer misfire yet.
Lifetime NRA Member