Typical failure modes are a collapsed lifter (the switching mechanism won't deactivate) or the roller failure (needle bearing failure). Either one can damage the camshaft lobe, but the roller failure will damage it to a greater extent.
There are other failures such as the locking pins not fully engaging causing the inner lifter to get stuck or lodged into the outer lifter body. This is a miss timed switching event. Technically this is also a collapsed lifter.
This video (1:00) talk about what happens. It is a good video in general on the lifter activation/deactivation cycle.
There could be a number of other failure modes but they are extremely rare.
Of course manufacturing defects can be a source of lifter failures. There was a bad batch in 2020 and 2021. These years seem to have a large representation in the failed lifter statistics.
There is another issue though...the engines that are higher in miles that fail with collapsed lifter or failed roller in the 60K-150K range. These failures also have a high occurrence of camshaft lobe damage.
This is where a defect may be unlikely as a cause for the typical failure modes.
Tolerance stacking may be afoot: a few pieces of the system may be at the extremes of their spec limit making it more sensitive to and prone to failure.
And it is also possible there are end-user issues.
When both are combined it can lead to a lifter failure earlier than expected.
Example.
Miles above 60K. Oil changes every 7000-7500 miles. lots of idle time in hot ambient conditions. 0w20. Oil temps at or above 220F for appreciable time.
The lube quality (viscosity, additive package degradation, acid number) is simply not adequate for keeping needle bearings from being at a point of incipient spalling.
Lube quality could be too poor for preventing spalling between cam lobe and roller.
Varnish can be causing lifter DFM cycle to be slow due to being gummed up. This can cause the miss timed switch event.
If a lifter had a tolerance stack issue on one or more component, the above operation would easily lead to early lifter failure.
I think these engines with DFM (in particular) are more sensitive to oil quality. Even without a tolerance stack issue, oil maintenance will put the lifter and cam at risk of early failure.
Example
Oil change interval 7500 miles on average. Sometimes 10K, 8K because life gets in the way and you can't get to a shop for an oil change. Most of the time it is changed at 7-7.5K. Always on 0W20. oil level not monitored. likely low on oil most of the time. Engine has 100K-150K miles. Lots of idle time waiting for kids at the game or school or in traffic jam.
Without the tolerance stack issue it will go further in miles before seeing same failure.
Throw in people who use the wrong oil (conventional mineral or even group III mineral, instead of group IV synthetic); or people who are absurdly intent on getting all they can out of their oil changes and go 10,000-12,000 miles (or 12 months)...and with the large customer base GM has with these engines, you are going to get a huge number of these types of errors...and associated early failures.
Putting the "Venn diagrams" together I have yet to see a significant number of these failure modes on engines managed by enthusiasts: people who will be changing oil at or before 5K miles, don't idle their vehicle excessively, use 5W30, do their own maintenance...any one of these categories seems to put their associated engines outside of the 60K-150K failure range. Combining any two of these seems to create a good safety factor against failure and shows up as a likely candidate for 200K+ miles before seeing these failures.
Specifically with Ram engines...I have experience with a 2017 Ram that just ate a lifter at 228,000 miles. Truck was used like a rented mule. Towed at max capacity 40% of the time. But the owner changed his own oil at 5000 miles, always used a good filter and full synthetic oil. But he used 0W20. He also complained all the time about getting oil temp warning lights and found that the truck usually had an oil temp of 230F. So with exceptional maintenance the system went 228,000 miles even on 0W20 at 230F.
