Pre-load with oil. Pre-load of oil.
The procedure with lifter in a container of oil, plunger pressed down to expel any trapped air then slowly release to intake only oil.
It's possible the valves were adjusted too tight squeezing the oil out. If so it may have lost it's pre-load of oil. There may be trapped air inside the lifters.
After some decent running time the trapped air may work itself out...fingers crossed.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."