You say proper assembly and break in.....but you didnt say the lifter bores were broached and the lifter checked for rotation at assembly. Are you sure this one was spinning good??
Cam and lifters job to do over either way.....no bueno.
They all spun freely when installing but we did not spin the full 360, prolly at best 180. They all went in relatively easy. I did a Cam /Lifter replacement on my BB 383 Dodge Charger years ago and had no problems, easy peasy..