So, lately I have noticed several types of, I guess, service sims hanging around in parks (mostly), often for hours on end casually chatting away with the townsfolk. I do not remember ever seeing that before (or maybe I just did not pay attention), but I have understood they are supposed to "come to do their service and then dissappear from the world", generally speaking. So far I have encountered a juice-pong loving repo-man, a chatty burglar, and a fire station worker, who did a lightningspeed whoosh while talking with him to figure out who he is. Some I have encountered several times over Sim days and weeks. As they are random EA-creations, they stand out (those outfits...) and are easy to recognize as "not my own". Also, I have not had any situations with my active household that would have made them appear, so I am wondering whether they "come to town" for inactives or just for fun.

So, is that normal and I have been oblivious to the fact for the past 15 years or am I having some strange bug?

That's normal.

Good to know, thank you!

it is called fake meta-autonomy. service sims either go to the park, festival ground, or bookstore rabbit hole from 9 to 18 all sim-days. if you're experienced in modding, you can edit the xml file with s3pe.