When performing a major or minor software upgrade of the HA pair, we expect to see a configuration mismatch after upgrading only one device in the pair. The mismatch is shown in the High Availability widget. The message that the running config is not synchronized is caused by the possible different layout of the XML configuration file in the new version.
The warning dissapears as soon as the upgrade procedure on the second peer finishes, when the software version on both peers is identical.