Frequent lifter collapse

[incola_malum]

I've picked up a 2000 XJ with a 4.6 stroker in it. By this time, I've replaced a lifter, then a cam and lifter, and looking at possibly another lifter soon. It appears that they keep collapsing. They throw codes for misfires on cylinders 1 and 4, with another code for random multiple misfires. Has anyone run into this before? I'm not sure what causes a lifter to collapse in the first place, frankly. This will be the third time I've replaced a lifter, however - and I'm interested in any insights this community might have so that I can fix it permanently.