Game freezes and fog of war covers already scouted parts of the map

This behaviour is completely random, but I get this every couple of hours.
While I'm playing, game freezes for 10-15 seconds, then it resumes, but all the map is covered in fog of war again. All loot and dead monsters are still there though.
This freeze can also occur in hideout, so it doesn't matter where player is at the moment.
Here a link to a video where the bug is shown. https://youtu.be/keZNdcmRlkE