Warning: Array to string conversion in /customers/7/9/d/larstragardh.se/httpd.www/wp-includes/post.php on line 5678

Fatal error: Uncaught TypeError: urldecode(): Argument #1 ($string) must be of type string, array given in /customers/7/9/d/larstragardh.se/httpd.www/wp-includes/post.php:5690
Stack trace:
#0 /customers/7/9/d/larstragardh.se/httpd.www/wp-includes/post.php(5690): urldecode(Array)
#1 /customers/7/9/d/larstragardh.se/httpd.www/wp-includes/rewrite.php(418): get_page_by_path(Array, 'OBJECT', 'post')
#2 /customers/7/9/d/larstragardh.se/httpd.www/wp-includes/class-wp.php(371): wp_resolve_numeric_slug_conflicts(Array)
#3 /customers/7/9/d/larstragardh.se/httpd.www/wp-includes/class-wp.php(780): WP->parse_request('')
#4 /customers/7/9/d/larstragardh.se/httpd.www/wp-includes/functions.php(1332): WP->main('')
#5 /customers/7/9/d/larstragardh.se/httpd.www/wp-blog-header.php(16): wp()
#6 /customers/7/9/d/larstragardh.se/httpd.www/index.php(17): require('/customers/7/9/...')
#7 {main}
  thrown in /customers/7/9/d/larstragardh.se/httpd.www/wp-includes/post.php on line 5690