This is only if it’s a hyd roller.......

Too much to type for the long version.........
Always happens right at start up?

I’ve had it happen here, and have talked to several others that have had the same thing happen.

The short answer is........try running more lifter preload.

From the point of where the plunger is preloaded to, to the plunger being bottomed out in the lifter...... has to be less distance than the depth of the adjuster screw cup in the rocker arm.

The adjuster cup is .120” deep.
Set the lifter preload so it’s .090”-.100” from being bottomed out.