When a hook throws an exception all other subscribers of the hook get also stopped.
Examples
mw.hook( 'wikipage.content' ).add( function ( $content ) { throw new Error( 'Foo' ); } );
blocks all extensions and gadgets that also use the hook 'wikipage.content'.
The reason for T220308 was an exception in Maps (Kartographer) that blocked MediaWiki-extensions-TocTree.
Expected behavior
An exception in a subscriber of a hook should not prevent that other subscribers of the hook gets fired.