Since the JSS 6 we can no longer run previews. Wether or not it's an issue I need to fix in the report (doubtful, these are all reports that work fine in 5.6.2).
We do have a custom provider class and library that we use.
With a simple "One empty record" report, there does not appear to be an issue.
### Update ###
Initially, JSS works just fine as intended. This occurs after a while and then becomes persistent. This feels quite similar to the bug in JSS 6.0.0 where the whole app just stops loading workbench after a few uses.
Start Report Execution
Setting Data Adapter...DONE
Report Execution Finished.
Maarten @ Yesplan