December 2019 - last edited January 2020
Product: The Sims 4
Which language are you playing the game in? Svenska
How often does the bug occur? Often (50% - 99%)
What is your current game version number? 18.104.22.1680
What expansions, game packs, and stuff packs do you have installed? All expansions, Dine Out, Vampires, Parenthood, Jungle Adventures, StrangerVille, Realm of Magic, Luxury Party Stuff, Kids Room Stuff, Holiday Celebration Pack, Grim's Ghoulish Guitar.
Steps: How can we find the bug ourselves? At least I think this is what caused the bug, since it worked fine before this. Have a sim living in a student dormitory and dropping out of university. Exit the lot before the moving out timer starts. Play with another family until the dormitory-sim can re-enroll at university. Go to the dormitory household and have the sim re-enrolling.
What happens when the bug occurs? Since the sim had dropped out of university the moving out timer will start even though the sim re-enrolled. Then you can't save, so you have to start an event (for example a dance party) at another lot (I found this workaround here on Answers HQ). After this, when the mail-deliverer comes with mail you get the normal notification that you got mail, but when you click on the mailbox the option to get the mail is greyed-out and when you hover over the option it says that there's no mail. It has happened 2 out of 3 times when the mail-deliverer came.
What do you expect to see? That the mail continues to arrive even under these weird re-enrolling circumstances.
Have you installed any customization with the game, e.g. Custom Content or Mods? Never used.
Did this issue appear after a specific patch or change you made to your system? No
I know this sounds weird, but I guess that this no-mail bug occurred because of me not moving out the sim from the dormitories before re-enrolling in university. I just didn't want to move out the sim out of convenience, since I was about to play another household anyway.
I've been playing with other sims in another dorm now, and it doesn't seem like the bug is due to the re-enrollment situation I first thought was the cause. The mail bug is there even in the other dorm.
I've kept a look on the mailbox and mail deliverer, and the mail is only delivered every third time the mail deliverer is there and you get a notification about mail every time the mail deliverer comes.