After successful attempt to update Redmine ( from 3.0.3 to 3.3.3 ) I tried to update Ruby version ( from 2.0.0 to 2.1.4 or 2.2.1 or 2.3.1 ) using rvm
The commands that I used are :

• rvm install 2.2.1 / 2.1.4 / 2.3.1
• rvm user --default 2.2.1 / 2.1.4 / 2.3.1
• cd /srv/redmine
• bundle update
• bundle exec rake db:migrate RAILS_ENV=production
• bundle exec rake redmine:plugins:migrate RAILS_ENV=production
• bundle exec rake tmp:cache:clear tmp:sessions:clear RAILS_ENV=production
• touch tmp/restart.txt

After doing those steps successfully, I encounter below error

[ 2017-03-10 11:42:09.6397 1680/7f1db50ec700 App/Implementation.cpp:303 ]: Could not spawn process for application /srv/redmine: An error occured while starting up the preloader.
  Error ID: f1f723b1
  Error details saved to: /tmp/passenger-error-NLN2oJ.html
  Message from application: <p>It looks like Bundler could not find a gem. Maybe you didn't install all the gems that this application needs. To install your gems, please run:</p>

  <pre class="commands">bundle install</pre>

<p>If that didn't work, then maybe the problem is that your gems are installed to <code>/var/www/.rvm/gems</code>, while at the same time you set <code>PassengerRuby</code> (Apache) or <code>passenger_ruby</code> (Nginx) to <code>/usr/local/rvm/wrappers/ruby-2.0.0-p643/ruby</code>. Because of the latter, RVM does not load gems from the home directory.</p>

<p>To make RVM load gems from the home directory, you need to set <code>PassengerRuby</code>/<code>passenger_ruby</code> to an RVM wrapper script inside the home directory:</p>

<ol>
  <li>Login as www-data.</li>
  <li>Enable RVM mixed mode by running:
      <pre class="commands">rvm user gemsets</pre></li>
  <li>Run this to find out what to set <code>PassengerRuby</code>/<code>passenger_ruby</code> to:
      <pre class="commands">/usr/local/rvm/gems/ruby-2.0.0-p643/wrappers/ruby \
/usr/bin/passenger-config --detect-ruby</pre></li>
</ol>

<p>If that didn't help either, then maybe your application is being run under a different environment than it's supposed to. Please check the following:</p>

<ol>
  <li>Is this app supposed to be run as the <code>www-data</code> user?</li>
  <li>Is this app being run on the correct Ruby interpreter? Below you will
      see which Ruby interpreter Phusion Passenger attempted to use.</li>
  <li>Please check whether the correct RVM gemset is being used.</li>
  <li>Sometimes, RVM gemsets may be broken.
      <a href="https://github.com/phusion/passenger/wiki/Resetting-RVM-gemsets">Try resetting them.</a></li>
</ol>

<p>-------- The exception is as follows: -------</p>
Could not find json-1.8.6 in any of the sources (Bundler::GemNotFound)
<pre>  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler/spec_set.rb:87:in `block in materialize&#39;
  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler/spec_set.rb:80:in `map!&#39;
  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler/spec_set.rb:80:in `materialize&#39;
  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler/definition.rb:176:in `specs&#39;
  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler/definition.rb:235:in `specs_for&#39;
  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler/definition.rb:224:in `requested_specs&#39;
  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler/runtime.rb:118:in `block in definition_method&#39;
  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler/runtime.rb:19:in `setup&#39;
  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler.rb:100:in `setup&#39;
  /usr/local/rvm/gems/ruby-2.0.0-p643/gems/bundler-1.14.5/lib/bundler/setup.rb:20:in `&lt;top (required)&gt;&#39;
  /usr/local/rvm/rubies/ruby-2.0.0-p643/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb:54:in `require&#39;
  /usr/local/rvm/rubies/ruby-2.0.0-p643/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb:54:in `require&#39;
  /usr/lib/ruby/vendor_ruby/phusion_passenger/loader_shared_helpers.rb:399:in `activate_gem&#39;
  /usr/lib/ruby/vendor_ruby/phusion_passenger/loader_shared_helpers.rb:277:in `block in run_load_path_setup_code&#39;
  /usr/lib/ruby/vendor_ruby/phusion_passenger/loader_shared_helpers.rb:404:in `running_bundler&#39;
  /usr/lib/ruby/vendor_ruby/phusion_passenger/loader_shared_helpers.rb:276:in `run_load_path_setup_code&#39;
  /usr/share/passenger/helper-scripts/rack-preloader.rb:99:in `preload_app&#39;
  /usr/share/passenger/helper-scripts/rack-preloader.rb:153:in `&lt;module:App&gt;&#39;
  /usr/share/passenger/helper-scripts/rack-preloader.rb:29:in `&lt;module:PhusionPassenger&gt;&#39;
  /usr/share/passenger/helper-scripts/rack-preloader.rb:28:in `&lt;main&gt;&#39;</pre>


[ 2017-03-10 11:42:09.6570 1680/7f1db60ee700 age/Hel/Req/CheckoutSession.cpp:252 ]: [Client 1-2] Cannot checkout session because a spawning error occurred.

I'm not too familiar with ruby & passenger but I think that my the passenger is still detecting ruby 2.0.0 as my main ruby installation ( even though rvm list already pointing into another ruby version )

Any help would be much appreciated :D