In order to investigate your issue we will need some more information like a sample app that reproduces the case and Fiddler log captured on your side.
To record a log please follow the steps below.
- Download Fiddler from here and install it.
- Run Fiddler and go to Tools -> Fiddler Options.
- On the HTTPS page, verify that Capture HTTPS Connects is enabled.
- Verify that Decrypt HTTPS traffic is enabled with the ...from all processes option and minimize Fiddler to tray.
- Run your AppBuilder client and open the app in the Simulator.
- When the error occur, in Fiddler, go to File -> Save -> All Sessions and save the archive to disk (a SAZ file).
- Send us the saz file and a sample project in a private ticket.
In the meantime try whether clearing the cache from %localappdata%\Telerik\BlackDragon\Cache helps.
I look forward to your reply.