For me, it's mostly been in medical settings. I've had particular trouble with public health programs automatically signing me up under my child's last name.
I don't know if my local healthcare catchment just has their software setup wrong, but it's a continual annoyance.
Even the assumption that people have (something that can be used as) a last name is incorrect.
Currently I'm living in Indonesia, where a surprisingly large number of people have just one name (plus, when they have many, they're more often than not completely arbitrary).
This was very common practice up to the '90s. If you have a single name, they duplicate it in your passport, and you end up like "Soekarno Soekarno". Which STILL raises eyebrows in several western countries' ignorant airline employees (and sometime even immigration officers, though they're admittedly more well educated about such issues).
Nowadays they proactively give at least two names to their children to match the western(-ized) system assumptions.
I don't know if my local healthcare catchment just has their software setup wrong, but it's a continual annoyance.