You've imported the app from Qlik Sense Desktop?
If so, you have to change your data connection if you're working with "lib" statement. (the data connection starts with lib://...)
If your data connection is an absolut path to some database/tables ,you have to go under engine, select your default one and desactivate standard mode to be able to use Absolut path connections with Qlik Sense Server
Hope this answers your question