about 2 years ago - CO_Avanya - Direct link
If you use Building Variations that mod is currently broken and causes buildings to become invisible. I also recommend you check your mods against the list of broken mods, both the first tab and especially the tab named P&P DLC Patch.
https://pdxint.at/BrokenModCS

If that doesn't help or you don't use mods, please make a thread on our support forum. We need to see your output_log.txt (called player.log on Mac and Linux) to be able to help, which cannot be attached here on Steam.
https://forum.paradoxplaza.com/forum/forums/support-bug-reports.879/

Windows
\SteamApps\common\Cities_Skylines\Cities_Data\output_log.txt
\CitiesSkylines\Cities_Data\output_log.txt

Mac OS X
Users//Library/Logs/Unity/Player.log

Linux
~/.config/unity3d/Colossal Order/Cities: Skylines/Player.log