View source for incompatible character encodings: UTF-8 and ASCII-8BIT

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[[page type::article]]
[[thing type::error message]]
[[category:error messages]]
[[category:Redmine]]
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'''ActionView::Template::Error (incompatible character encodings: UTF-8 and ASCII-8BIT)''' is an error message which was encountered in [[Redmine]] 3.2.1.stable.

It's possible this problem is related to [https://medium.com/@adamhooper/in-mysql-never-use-utf8-use-utf8mb4-11761243e434 this issue with MySQL].
==Pages==
* [[/2011-11-13 Askru post]]
==Encounter Details==
Environment:
<pre>
Environment:
  Redmine version                3.2.1.stable
  Ruby version                   2.3.1-p112 (2016-04-26) [x86_64-linux-gnu]
  Rails version                  4.2.6
</pre>
Error message:
<pre>
Started GET "/issues/217" for 107.15.53.219 at 2020-02-04 02:00:26 +0000
Processing by IssuesController#show as HTML
  Parameters: {"id"=>"217"}
  Current user: woozle (id=4)
  Rendered issues/_action_menu.html.erb (4.7ms)
  Rendered issue_relations/_form.html.erb (1.4ms)
  Rendered issues/_relations.html.erb (2.2ms)
  Rendered issues/_history.html.erb (11.2ms)
  Rendered issues/show.html.erb within layouts/base (46.9ms)
Completed 500 Internal Server Error in 121ms (ActiveRecord: 30.4ms)

ActionView::Template::Error (incompatible character encodings: UTF-8 and ASCII-8BIT):
    121: <% if @journals.present? %>
    122: <div id="history">
    123: <h3><%=l(:label_history)%></h3>
    124: <%= render :partial => 'history', :locals => { :issue => @issue, :journals => @journals } %>
    125: </div>
    126: <% end %>
    127: 
  app/views/issues/show.html.erb:124:in `_app_views_issues_show_html_erb___1920726361900740288_70338122766120'
  app/controllers/issues_controller.rb:118:in `block (2 levels) in show'
  app/controllers/issues_controller.rb:115:in `show'
  lib/redmine/sudo_mode.rb:63:in `sudo_mode'
</pre>