A Google Maps key that renders correctly when installed can stop working months later, even though nothing on your website has changed.
Why this happens. Google requires an active billing account to serve map tiles, even when your usage is within the free monthly allowance. If billing lapses, or if a billing account is detached from your Google Cloud project, the map stops working. No change on the website side is needed for this to happen.
What you can do. Check the browser console for the specific error message. It tells you what needs to be fixed in your Google Cloud project.