If the On-Demand buttons stopped working... yes you can restarting the SER service ... to solved the problem!
But we found a issue at the last Reporting Suite Version of "5.1.6".
To solve the issue:
Please update the Reporting Suite to 5.1.8 - direct download: https://info.analyticsgate.com/asset/23:analyticsgate-current-version-reporting
and add this new rule to the Qlik Sense security rules settings: