If you don’t have child theme active from start, and activating it sometime later,
customizer settings set while on main theme do not get implemented on child theme.

Nothing to worry, this is how customizer is expected to work 🙂
Can be fixed withing a minute.

• Just shift to main theme
• Install – Customizer Export/Import plugin OR any similar plugin could be used.
• Go to : Customize > Export/Import
• Get ‘Export’ file of custmizer
• Activate child theme.
• ‘Import’ the file we have taken while on main theme.
• Done