Passenger 'loses' rack after apt-get-upgrade - passenger

Question

everything was running fine before I did an apt-get upgrade.
afterwards, passenger refuses to start with the following in /var/log/nginx/access.log
<p>-------- The exception is as follows: -------</p>
Could not find rake-12.3.0 in any of the sources (Bundler::GemNotFound)
<pre> /usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler/spec_set.rb:88:in `block in materialize'
/usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler/spec_set.rb:82:in `map!'
/usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler/spec_set.rb:82:in `materialize'
/usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler/definition.rb:170:in `specs'
/usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler/definition.rb:237:in `specs_for'
/usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler/definition.rb:226:in `requested_specs'
/usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler/runtime.rb:108:in `block in definition_method'
/usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler/runtime.rb:20:in `setup'
/usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler.rb:107:in `setup'
/usr/local/rvm/gems/ruby-2.4.0#global/gems/bundler-1.16.1/lib/bundler/setup.rb:20:in `<top (required)>'
/usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/usr/lib/ruby/vendor_ruby/phusion_passenger/loader_shared_helpers.rb:456:in `activate_gem'
/usr/lib/ruby/vendor_ruby/phusion_passenger/loader_shared_helpers.rb:323:in `block in run_load_path_setup_code'
/usr/lib/ruby/vendor_ruby/phusion_passenger/loader_shared_helpers.rb:461:in `running_bundler'
/usr/lib/ruby/vendor_ruby/phusion_passenger/loader_shared_helpers.rb:322:in `run_load_path_setup_code'
/usr/share/passenger/helper-scripts/rack-preloader.rb:100:in `preload_app'
/usr/share/passenger/helper-scripts/rack-preloader.rb:156:in `<module:App>'
/usr/share/passenger/helper-scripts/rack-preloader.rb:30:in `<module:PhusionPassenger>'
/usr/share/passenger/helper-scripts/rack-preloader.rb:29:in `<main>'</pre>
[ E 2018-02-27 19:09:48.8581 1603/T8 age/Cor/Con/CheckoutSession.cpp:285 ]: [Client 1-2] Cannot checkout session because a spawning error occurred. The identifier of the error is ed1f1d19. Please see earlier logs for details about the error.
App 2674 stdout:
App 2674 stdout:
[ E 2018-02-27 19:10:18.7891 1603/Tn age/Cor/App/Implementation.cpp:304 ]: Could not spawn process for application /home/webuser/sites/recruit_production/current: An error occurred while starting up the preloader.
Error ID: 1efd19d8
Error details saved to: /tmp/passenger-error-t9Edn6.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 the problem is probably caused by your application 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>webuser</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>
</ol>
however rake-12.3.0 does seem to be installed
$ sudo find / -type d -iname "rake-12.3*"
/home/webuser/sites/recruit_production/shared/bundle/ruby/2.4.0/gems/rake-12.3.0
/opt/chef/embedded/lib/ruby/gems/2.3.0/gems/rake-12.3.0
where should I be looking to figure this out???
webuser is the correct user, and ruby 2.4.0 is also correct
I'm using RVM on ubuntu
thanks in advance