So yesterday i upgraded Qlik Sense Server to june 2019 version. After that, i tried to reload an application but it directy fails. The error was the application was unable to read the data source.
So, if you have a multi node deployement, the solution for that is :
Go to Schedulers in " Configure System" then make the central node "Slave" (in Advanced, Type) and the Frontnode "Master". Apparently, by default, when you're upgrading Qlik Sense Server, thoses types changes.