With the latest version of Umbraco CMS 12.22.1 when you are using a LinkDataCollection, if you choose to "Select Content" rather than "Create a new link" then the modal that appears is showing as empty and no tree-view is showing. This has been tested on a fresh install of the Alloy demo site.
With the latest version of Umbraco CMS 12.22.1 when you are using a LinkDataCollection, if you choose to "Select Content" rather than "Create a new link" then the modal that appears is showing as empty and no tree-view is showing. This has been tested on a fresh install of the Alloy demo site.