There is nothing wrong with the linked PHP, however the issue could be stemming from another field group.
Are you able to debug the JS?
1. Copy the contents from js/input.js
2. Replace the contents of js/input.min.js
3. Find the line with if( acf.helpers.isset( this.toolbars[ this.o.toolbar ] ) )
3. Before this line, console.log the variables such as this.o.toolbar
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