Metabase cannot parse geo-JSON anymore

With recent Metabase Upgrades a custom geo-JSON file can no longer be opened.

Metabase claims that the features key would be null - though in the file (see the link) it is clearly defined and filled with some values.

How can I create a geo-JSON which works with Metabase (in the current version of Metabase)? Or can Metabase be fixed?