The Save button is greyed out when enabling or disabling the Process Isolation setting in Data Gateway. This issue only occurs when the Gateway has been upgraded from older versions.
Resolution
Log in to your Qlik Cloud tenant and open the Administration Console
Navigate to Data Gateways and open the Data Gateway experiencing the issue
Open each connector (ODBC, SAP, REST, and similar), and modify the Number of concurrent reload processes to a value between 2 and 100.
This must be done on all connectors, even if they are not actively used.
Change Process Isolation; the Save button is now available.