Mostly domestic, I have 1 or 2 problems a year out of 70-90 nights. It's almost always a missing PLT amenity. A note on the website to customer support usually fixes it, though it took two communications to correct a stay at the Cosmopolitan this year. They also took 10 days to post vs. the typical 2-3, and seem to have a reputation for falling down in this area.

I have 75 nights so far 20 years and 1600+ nights. This year 1 time, over the years on average 1 time per year.

I've seldom had a problem with domestic (Stateside) stays posting correctly, but overseas stays, particularly when using Bonus Bucks, were quite a problem.

Even then, though, it seemed to be a problem only with certain properties, not others in the same city, so it could simply be that specific properties just don't know how to set it up correctly.

This tends to match my experience as well. I don't usually have any issues with US based stays posting correctly, but some of my non-NA (primarily in the UK) have issues posting correctly.

1/20 are not posting for me and all of them post with the correct # of points. I am booking all my stays through Marriott.com which I am sure helps.

I don't understand why the change for me. Almost half of my stays this year have had some sort of issue.
Most have involved the plat welcome gift, but I have had 4 stays not credit at all. And I book almost all of my stays through Marriott.com or our corporate travel site.
Two biggest issues seem to be around stays at Autograph Collection hotels and when the property has a Rewards Bonus Point rate.
Maybe I just need to stick to standard rates.