I am sorry to hear you experience an issue with this functionality. It is possible to be a caching problem, would you try clearing AppBuilder's Cache at your side - you'll find it under the %localappdata%\Telerik\BlackDragon
folder. Please remove the entire Cache
In case there is still a problem, may I ask you to send us the following information:
1. The AppBuilder logs located at %LOCALAPPDATA%\Telerik\BlackDragon\Logs (please create an archive of the entire folder and attach it to the ticket)
2. A Fiddler capture of the Telerik Platform requests, which you can gather following the instructions described here.
In order to keep any sensitive information private, you can open a new support ticket and send the logs there. That way we can examine them and will be able to advice better.