Drupal 8 nginx "Place blocks" error

Uncaught AjaxError: 
An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /admin/structure/block/library/fsl_theme?region=header
StatusText: OK
ResponseText: 
Place block | Financing Sustainable Landscapes
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{"ajaxPageState":{"theme":"seven","libraries":"admin_toolbar\/toolbar.tree,admin_toolbar\/toolbar.tree,admin_toolbar_tools\/toolbar.icon,admin_toolbar_tools\/toolbar.icon,block\/drupal.block,block\/drupal.block.admin,block\/drupal.block.admin,classy\/base,classy\/base,classy\/messages,classy\/messages,coffee\/drupal.coffee,coffee\/drupal.coffee,contextual\/drupal.contextual-links,contextual\/drupal.contextual-links,contextual\/drupal.contextual-toolbar,contextual\/drupal.contextual-toolbar,core\/drupal.active-link,core\/drupal.active-link,core\/drupal.dropbutton,core\/drupal.dropbutton,core\/drupal.tabledrag,core\/drupal.tableheader,core\/drupal.tableresponsive,core\/drupal.tableresponsive,core\/html5shiv,core\/html5shiv,core\/normalize,core\/normalize,seven\/drupal.nav-tabs,seven\/global-styling,seven\/global-styling,shortcut\/drupal.shortcut,shortcut\/drupal.shortcut,toolbar\/toolbar,toolbar\/toolbar,toolbar\/toolbar.escapeAdmin,toolbar\/toolbar.escapeAdmin,tour\/tour,tour\/tour,user\/drupal.user.icons,user\/drupal.user.icons","theme_token":"ZB2s1dvLFeO3ag3lj4J7QIteVlZGJOWzpSHj8sm77MU"},"coffee":{"maxResults":7},"toolbar":{"breakpoints":{"toolbar.narrow":"only screen and (min-width: 16.5em)","toolbar.standard":"only screen and (min-width: 38.125em)","toolbar.wide":"only screen and (min-width: 61em)"},"subtreesHash":"0CqwYuaH0mImlqag4hvK6cET3y0D0zxprdXN4BKjIb0"},"path":{"baseUrl":"\/","pathPrefix":"","currentPath":"admin\/structure\/block\/library\/fsl_theme","currentPathIsAdmin":true,"isFront":false,"currentLanguage":"en"},"pluralDelimiter":"\u0003","user":{"uid":"1","permissionsHash":"aaef1b444ab90173508b9e3ad08eb293bc5139f4d13d545824ba730122138516"}}