Rank Math SEO - Fatal Error with HTML Sitemap

Overview of the issue

A fatal error occurs when using the HTML sitemap feature from the Rank Math SEO plugin via a shortcode, [rank_math_html_sitemap].

Fatal error: Uncaught TypeError: Cannot access offset of type string on string in .../wp-content/plugins/wp-seo-multilingual/classes/RankMathSEO/Sitemap/Hooks.php on line 69

Workaround

Please, make sure of having a full site backup of your site before proceeding.

• Edit …/wp-content/plugins/wp-seo-multilingual/classes/RankMathSEO/Sitemap/Hooks.php file.
• Just before line 66:

  		return Obj::assoc(
  			'loc',
  			Obj::propOr(
  				$url['loc'],
  				(int) Obj::prop( 'ID', $object ),
  				$this->secondaryHomesById
  			),
  			$url
  		);
  

• Add this code:

  		if (!is_array($url)){
  			$test = $url;
  			$url = array();
  			$url['loc'] = $test;
  		}