I'm getting the following error when validating a change set with a new custom app in it:
Error parsing file: 'Background' is not a valid value for the enum 'FlexiPageRegionType'
It seems to be suggesting that it is a problem with a UtilityBar component, but I don't have that activated for my app.
I have noticed that my sandbox has updated to Winter '19 but the destination is still Summer '18.
I cannot see how to force the sandbox to Winter '19.
Any help would be greatly received.