No problems with my flat tappet Comp Cam I put in several years ago. I did take extraordinary measures to break it in. As I recall the first 20 minutes after the first start up determine whether a flat tappet cam will live or die, you usually find out in the near future following that.
I'm wondering what steps were taken during the dyno break in to assure a long life? Removal of the inner springs? Break in rocker arms? Holding the rpm at or above 2,000 rpm for those first 20 minutes? If it went straight to the dyno without any special mechanical attention to break in, there's the problem! For an engine builder, doing any of the above is a real pita, it takes up a lot of time and eats directly into the profit margin. That is why so many builders won't even offer a flat tappet anymore, just to much hassle and risk if you don't get it right.
Hotfingers, roller lifters don't generally require any special mechanical attention for break in. Wierd you had a run of bad luck, I don't know what to make of it. Some years ago ALL the cam manufacturers were having problems with flat tappets, which was eventually traced, primarily, to the changes in
oil available. That remains an issue, but of far less concern with the roller lifters, then or now,,, strange. Another factor, then and it remains an issue, is low quality lifters, perhaps made in China sort of thing. A large number of cam failures, some years ago, were a direct result of readily available cheap and inferior lifters.