I've had several. All of them have been my own reloads and generally fall into a category of loads.
I (used to) shoot Bullseye. I cannot find a local match these days. I have a .45 ACP 'wadcutter' pistol. While experimenting with ultra light loads, some where too light. I had a similar problem with a .38 Special PPC revolver.
I was fire-forming some brass (.30-06 to .30-06 Scott's Improved) and one bullet stopped with the nose exactly at the end of the muzzle.
Nothing too serious, but annoying.
Cannot remember any factory squibs. Had some problems with .22 rimfire ammunition not firing at all.