Can't build basement & saving issues

Product: The Sims 4
Platform:PC
Which language are you playing the game in? Deutsch
How often does the bug occur? Every time (100%)
What is your current game version number? 1.103.315.1020
What expansions, game packs, and stuff packs do you have installed? all, except the wedding game pack
Steps: How can we find the bug ourselves? Building a basement in the highschool lot (and trying to save afterwards)
What happens when the bug occurs? The basement is not build and saving the game afterwards is in an endless loop, where you have to force close the game. Nothing is saved.
What do you expect to see? A fix, so that I can build a basement and especially, that the game saves normally and I don't lose any progress.
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? Neutral/Not Sure 

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Hi there,

I haven't really played Sims 4 in some time and then started again in December after the For Rent pack came out.

After building some appartement building (without basement) I wanted to build a new highschool for my teenager, but I have some troubles with that:

1. I can't build any basement there (not sure if it is only on that lot or everywhere): neither with the basement tool from the ground floor, nor by copying a room and trying to place it in the basement level or by building a new room there. Nothing at all happens. No error message, no basement, no red lines nor anything. Its independent on where I build the basement on the lot.

2. Saving seems mostly to work, except after I try to build a basement. Then the "saving" is there for a long time and nothing happens. I have to force quit the game then, and nothing is saved. This happend as well one time without a basement, so might not be 100% related to the basement?

Has anyone else the problem as well? Any advice on how to fix this?