When using a JSON file as the map data source, some of the tooltip visual options will not work, like the maximum width option. To workaround this you can wrap your tooltip template option with a div with a custom class:
This way you can target that class to fix any visual issues. For example:
.map_wrapper .custom-tooltip { max-width:200px !important; white-space:normal !important; line-height:1em; }