Lifters can internally varnish until they stick. Either synthetic oil can help or a quart of transmission fluid in the base oil.

With lifters other than the ones that are dirt cheap. I number when removing them. Then pump them up with a drill press in tray a of light oil. Seeing how they compare to a new one.

If not I take them apart and clean them. Then retest. If they then test as good as new there is no wear.

I am not suggesting this is your problem.