When upgrading, all the remote scanners simultaneously restart, bringing the appliances out of production. What can be done in order to prevent this behavior when upgrading the Finjan to a newer software version?

In order to update each scanner separately and avoid simultaneous scanner restarts, please browse to the management console of the appliance and then click on the Settings tab -> Devices -> Policy Server -> VSOS Updates -> Click the Update selected Scanning Servers -> Apply and commit changes, as depicted in the screenshot below: