Guys, remember that Comp outsources their lifters and camshaft cores just like everyone else. So saying that Comp cams or lifters are crap just because they're Comp indicates your ignorance.

Or maybe I should tell you how I really feel.........

R.

TTI warns users to NOT break in a new build/cam with their headers installed.

Did you actually measure the bores and lifters to get lifter-to-bore clearance?
There is much more potential for a problem either with the lifter bore machining in the block or with lifter bore wear, then with a production problem with a specific brand of lifter or camshaft. The problem becomes the angle that the lifter hits the face of the lobe is allowed to deviate some. It doesn't take much to have it be wrong, and to have a failure. Think about how (cough...cough...) accurate the rest of the block machining from the factory was.
I think you have a block that has some wear, and possible angle issues with the lifter bores. It's not uncommon at all but ask around and see how many shops/builders check for clearance (I do) or bore accuracy (I typically won't unless there's a history to warrant it) during the block machining phase. In most cases the care and process will allow things to work fine over a long service life. in other cases they may have one or some that are so bad it only takes a minor increase in cam size and required spring pressures before a problem surfaces. Things such as too little or too much preload, loss of valve train control due to improperly set valve spring heights, and weak pushrods can also cause cams to give up.

Eddie Miller told me several years ago that Comp gets its cores from the only two places that supply them. If you bought a shelf grind, the cores came from one budget vendor. If you spec'd a custom grind, the cores came from a different/better vendor. IIRC, he said Crane was the better supplier.