Google updated the FAQ section of the 'Syncing your products' GMC Help documentation to clarify what to do during the upcoming Content API --> Merchant API migration concluding by August 18.

• Don't uninstall & reinstall the Google & YouTube Shopify app
• Google knows there are issues with it and is working with Shopify to fix them
• Google said there's no action needed - if you use the Google & YouTube app on Shopify to manage your GMC feeds, they will handle the API transition for you