You can run into this issue if you have a malformed custom theme file. If you are running into this issue, can you post or link to your complete theme file JSON? I see "osme" found how you can fix bad theme files. 🙂
^ as you can see from the link, propertyValue should never be an array. It should either be a number, boolean, string, or a color definition. We're in the process of rolling out a fix to revert our stricter parsing logic this week, but theme files can be fixed immediately to mitigate this issue.