When you delete a Character property sometimes it still is expected when you run or load a project that it once existed and an error will display mentioning the property is missing.
I tried closing Dev and re-opening it and the project but problem does not go away. I can confirm if its a character, deleting all the characters with that property and creating the characters again and re-selecting the properties fixes this. However that would be a lot of work in a large project.
I have had similar problems with objects in the past too.