I have had a hangfire, but it wasn't for a long stretch. It was more like a click-BANG. Happened twice with the same loads, so I stopped after the second one and pulled the rest of the loads apart.

This was in .460 S&W Magnum and while I cannot be certain, I believe the issue was far too little crimp which allowed the slug to jump forward from the primer blast. My other theory was that I might have had tumbling media stuck in the flash hole which greatly impeded the flame from the primer.

I'm not 100% sure, but it was a scary wake-up call.