change how author is assigned, use site.author

_includes/author-profile.html

 <!-- {% assign author = page.author | default: page.authors[0] | default: site.author %} -->
-{% unless page.author %}
-  {% assign author = page.url | split: "/" %}
-  {% assign author = author[1] %}
-{% endunless %}
-{% assign author = site.data.authors.authors | where: "prefix", author | first %}
+{% assign author = site.data.authors.authors | where: "prefix", site.author | first %}
 
 <div itemscope itemtype="https://schema.org/Person">
 

_includes/seo.html

@@ -26,9 +26,7 @@
 {%- endif -%}
 
 <!-- don't use page.author even if it is set, find author based on url -->
-{% assign author = page.url | split: "/" %}
-{% assign author = author[1] %}
-{% assign author = site.data.authors.authors | where: "prefix", author | first %}
+{% assign author = site.data.authors.authors | where: "prefix", site.author | first %}
 
 {%- if author.twitter -%}
   {%- assign author_twitter = author.twitter | replace: "@", "" -%}

_layouts/single.html

@@ -2,11 +2,7 @@
 layout: default
 ---
 
-{% unless page.author %}
-  {% assign author = page.url | split: "/" %}
-  {% assign author = author[1] %}
-{% endunless %}
-{% assign author = site.data.authors.authors | where: "prefix", author | first %}
+{% assign author = site.data.authors.authors | where: "prefix", site.author | first %}
 
 {% if page.has_header %}
   {% include page__hero.html %}
@@ -19,6 +15,7 @@ layout: default
 {% endif %}
 
 <div id="main" role="main">
+coucou
   {% include sidebar.html %}
 
   <article class="page" itemscope itemtype="https://schema.org/CreativeWork">