Redmine

When I save an update (let's say for redmine_mail_checker although I've seen the same problem for redmine_knowledgebase), the settings are cleared instead of being saved.

Here is the system info:

Environment:
  Redmine version                3.4.3.stable.17121
  Ruby version                   2.4.1-p111 (2017-03-22) [x86_64-linux]
  Rails version                  4.2.8
  Environment                    production
  Database adapter               Mysql2
SCM:
  Subversion                     1.8.8
  Git                            1.9.1
  Filesystem                     
  GitRemote                      1.9.1
Redmine plugins:
  redcase                        1.0
  redmine_checklists             3.1.5
  redmine_code_review            0.9.0
  redmine_git_remote             0.0.1
  redmine_knowledgebase          3.2.1
  redmine_mail_checker           1.0.0

Here is a sample log entry:

Started POST "/settings/plugin/redmine_mail_checker" for <ip address> at 2017-12-29 13:00:54 -0800
Processing by SettingsController#plugin as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"xxxx", "settings"=>{"protocol"=>"pop3", "host"=>"", "port"=>"", "ssl"=>"false", "username"=>"", "password"=>"[FILTERED]", "folde$
Current user: jlee (id=3)
Redirected to https://redmineurl/settings/plugin/redmine_mail_checker
Completed 302 Found in 33ms (ActiveRecord: 15.4ms)
Started GET "/settings/plugin/redmine_mail_checker" for 192.168.237.85 at 2017-12-29 13:00:55 -0800
Processing by SettingsController#plugin as HTML
Parameters: {"id"=>"redmine_mail_checker"}
Settings cache cleared.
Current user: jlee (id=3)
Rendered plugins/redmine_mail_checker/app/views/settings/_common_options.html.erb (1.8ms)
Rendered plugins/redmine_mail_checker/app/views/settings/_imap_options.html.erb (0.6ms)
Rendered plugins/redmine_mail_checker/app/views/settings/_pop_options.html.erb (1.1ms)
Rendered plugins/redmine_mail_checker/app/views/settings/_redmine_options.html.erb (0.6ms)
Rendered plugins/redmine_mail_checker/app/views/settings/_redmine_mail_checker.html.erb (5.6ms)
Rendered settings/plugin.html.erb within layouts/admin (7.8ms)
Rendered admin/_menu.html.erb (6.8ms)
Rendered plugins/redmine_code_review/app/views/code_review/_html_header.html.erb (0.1ms)
Rendered inline template (1.3ms)
Rendered plugins/redmine_code_review/app/views/code_review/_body_bottom.html.erb (0.1ms)
Rendered layouts/base.html.erb (45.0ms)

Any idea of what might be happening?