First of all, save your game while you are experiencing graphical problems. Close the game and please make sure that the Texture Compression of the game is turned off. You can check this in Steam by right-clicking on the game in your library, then select the Visionaire Configuration Tool. In there, you can disable the Texture Compression. After this, you should be able to play the game properly and load the savefile without having to deal with any graphic glitches.
If the issue isn't solved by turning Texture Compression off, please check whether you are using the latest graphic card driver. Very often outdated drivers are the source of a variety of problems in our games. The best way to update your driver is looking directly at the manufacturer's page of your graphics card. Since automatic Windows updates do not always find the latest drivers, we recommend looking for them manually.