You can manually type the property name and submit the modal dialog, it gets saved perfectly fine. Or either open the portal in any other browser, you can see the properties on click of down arrow.
This an existing issue in chrome browser alone when there are any pages/parameters defined for that rule you see this issue, you can also install the hotfix to fix it as mentioned in the below link according to your product version.
In the error.png file I see that the grid is being sourced by a Report definition but your requirement is from a Data page. Also try giving the reference of the Data Page in the Pages&Classes tab of the Section. You should be able to get the property value.