How do hydraulic flat tappet lifters fail?

Thanks furry, I'll take your advice. This was my first build, and honestly, I didn't prime the engine until it was fully assembled. I used plenty of assembly lube, but I didn't prime for oil pressure until later. By then, obviously it was too late to see what the lifters were doing. This is all a great learning process, and hopefully with experience and practice, I'll get this down!