This bug was on the old forums with a lot of reports, but I can't find it here.
This sounds similar to this bug, but it's not.
With this bug, you may build for a while and then all of a sudden, your fountain (for example) won't place. No matter what you do, nothing will place. selecting another tool won't fix it.
If you try to save or go to manage worlds, you ALWAYS will get an endless saving/loading screen.
This bug can also occur on a specific lot. The "The Old Salt House" lot in San Myshuno was a problem for me every time I loaded into the lot and tried to build. It would never go through. It happened right away.
This specific lot may not be a problem for everyone. Once, I had the same issue for a lot in Brindleton Bay, but with an update, that lot wasn't having that issue anymore.
I had this happen many of times and I believe it started with the patch before For Rent.
Here's the link I have for the old forum, I don't know if anyone will have access to it though: https://t.co/4xoNY24q7n
More info: I have all the packs and I'm on the latest update.
Save File: https://drive.google.com/drive/folders/1nu4JrOjJlMc20V2hNLi1FOoCf2pufqu8?usp=sharing
I use CC and Mods, but I can ensure you that's not the issue.
I had this issue yesterday as well and I waited for 10 minutes before force quitting. Video attached below.