Ajax Error

On a newly installed drupal instance, I cannot place blocks.
Server : Lighttpd/ Kubuntu 17.10 server, Drupal 8.4.4, no content added (this is a new installation installed especially to investigate the problem which had occurred on another site)

At: admin/structure/block - Header -> Place block --> times out --> then the browser console shows message below
There are no log messages, no server error messages
Suspect it could be due to lighttpd. Increased PHP timeout etc., with no effect

In console:

Drupal.AjaxError {message: "↵An AJAX HTTP error occurred.↵HTTP Result Code: 20…10be6325a45766c8abfe9f6eeb85e5648e3bfd507eb58"}}↵", name: "AjaxError"}
message
:
"↵An AJAX HTTP error occurred.↵HTTP Result Code: 200↵Debugging information follows.↵Path: /admin/structure/block/library/bartik?region=header↵StatusText: OK↵ResponseText: ↵Place block | admin↵Skip to main content↵Toolbar items↵Back to site↵Manage↵Administration menuContentStructureAppearanceExtendConfigurationPeopleReportsHelp ↵Shortcuts↵User-defined shortcutsAdd contentAll contentEdit shortcuts ↵Edit↵Tour↵admin↵User account actionsView profileEdit profileLog out ↵Place block↵Add to Default shortcuts↵Breadcrumb↵Home↵Administration↵Structure↵Block layout↵Add custom block↵Filter↵Block↵Category↵Operations↵Page title↵core↵Place block↵Primary admin actions↵core↵Place block↵Tabs↵core↵Place block↵Search form↵Forms↵Place block↵User login↵Forms↵Place block↵Help↵Help↵Place block↵Recent comments↵Lists (Views)↵Place block↵Recent content↵Lists (Views)↵Place block↵Who's online↵Lists (Views)↵Place block↵Administration↵Menus↵Place block↵Footer↵Menus↵Place block↵Main navigation↵Menus↵Place block↵Shortcuts↵Menus↵Place block↵Tools↵Menus↵Place block↵User account menu↵Menus↵Place block↵Breadcrumbs↵System↵Place block↵Main page content↵System↵Place block↵Messages↵System↵Place block↵Powered by Drupal↵System↵Place block↵Site branding↵System↵Place block↵Syndicate↵System↵Place block↵Who's new↵User↵Place block↵{"ajaxPageState":{"theme":"seven","theme_token":"owMjX-41_Pcx... removed ... KjyZ5xKq0gw","libraries":"block\/drupal.block,block\/drupal.block.admin,block\/drupal.block.admin,classy\/base,classy\/base,classy\/messages,classy\/messages,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"},"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":"q5SbYHg6y4...removed.... K47EstXN08M"},"path":{"baseUrl":"\/","pathPrefix":"","currentPath":"admin\/structure\/block\/library\/bartik","currentPathIsAdmin":true,"isFront":false,"currentLanguage":"en","currentQuery":{"error":"404"}},"pluralDelimiter":"\u0003","user":{"uid":"1","permissionsHash":"744e0258b..removed.3bfd507eb58"}}↵"
name
:
"AjaxError"
__proto__
:
Error at https://www.drupalservertest.com/sites/default/files/js/js_5YKInKTXfkhKH... at https://www.drupalservertest.com/sites/default/files/js/js_5YKInKTXfkhKH...
constructor
:
ƒ (xmlhttp, uri, customMessage)
stack
:
"Error↵ at https://www.drupalservertest.com/sites/default/files/js/js_5YKInKTXfkhKH...↵ at https://www.drupalservertest.com/sites/default/files/js/js_5YKInKTXfkhKH..."
__proto__