new lazy lifter....
FWIW... been seeing soft hydraulic lifters of various sorts for 15 years now or thereabouts. Last was some on a Crane cam in a 340.....not the slowest ramp cam around but not fast for sure, and moderate springs (just under 300 lbs open). 2 lifters went soft in <1000 miles. Replaced. Never used to have to do this back in the day. Raced OEM hydraulics in an Opel CIH to over 7500 RPM all day long... never a peep from them.
Lighter oils make the symptoms worse, but I'd rather run the oil that is best for the rest of the engine and let the lifters chatter.