If you don’t play for 28 days straight, the game will slowly start selling your venues. After 10 more days, your whole portfolio will be sold out. Logging in even once during this time stops the whole process.
We introduced this feature in order to keep the game playable. Otherwise, inactive players would block properties forever in their portfolio, preventing active players from being able to purchase them.
Cash from sold out properties is added to the player's empire, allowing player to rebuild a previous empire with this money.