We have a Bug that prevents the Upgrade to work properly in versions 3.1.X,
Also the settings backup are intended to be restored in the same version from where they were taken, not in a different version of the CAS.
Version 22.214.171.124 is available which is recommended to upgrade to, if the issue is encountered again our recommendation is to perform a Reset to Factory Defaults in the new version and set up the configuration of the CAS manually.
Use method 2 of the link to restore the appliance to factory defaults,
Please let us know if you have any other questions that we could answer for you.