At first i could open 2 apps and accessed to data load editor by using QlikSense Hub.
After that i could still open the 3rd app, but i couldn't go through data load editor.
I had checked it and it positiviely was not because of the security rules.
The message error that showed up was "The REST connection has failed." while the data visualization on the 3rd app was perfectly fine.
The situation applied to all apps because it was still happening even i did it randomly.
Actually it happened only if the apps belong to 1 stream.
If the 3rd app belongs to other streams, even the data visualization would not show up. It just instantly gave me "The REST connection has failed."
Hope you can give me the answer or answer of related issue.
Thankyou for your assistance and support.