1-Click RoR: Unicorn loops - Refreshing Gem list

I am running on 1-Click RoR: Ruby 2.1.3, Rails 4.1.6, Unicorn 4.9.0, RVM 1.26.11.

My app was running fine until I have update Ubuntu and after server restart Unicorn uses 100 % CPU and in the log I have found repeating this:

/usr/local/rvm/rubies/ruby-2.1.3/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- bundler/setup (LoadError)
from /usr/local/rvm/rubies/ruby-2.1.3/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/rails/config/boot.rb:4:in `<top (required)>'
from /usr/local/rvm/rubies/ruby-2.1.3/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/local/rvm/rubies/ruby-2.1.3/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/rails/config/application.rb:1:in `<top (required)>'
from /usr/local/rvm/rubies/ruby-2.1.3/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/local/rvm/rubies/ruby-2.1.3/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/rails/config/environment.rb:2:in `<top (required)>'
from /usr/local/rvm/rubies/ruby-2.1.3/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/local/rvm/rubies/ruby-2.1.3/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from config.ru:4:in `block in <main>'
from /usr/local/rvm/gems/ruby-2.1.3/gems/rack-1.5.5/lib/rack/builder.rb:55:in `instance_eval'
from /usr/local/rvm/gems/ruby-2.1.3/gems/rack-1.5.5/lib/rack/builder.rb:55:in `initialize'
from config.ru:1:in `new'
from config.ru:1:in `<main>'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/lib/unicorn.rb:48:in `eval'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/lib/unicorn.rb:48:in `block in builder'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/lib/unicorn/http_server.rb:768:in `call'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/lib/unicorn/http_server.rb:768:in `build_app!'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/lib/unicorn/http_server.rb:632:in `init_worker_process'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/lib/unicorn/http_server.rb:655:in `worker_loop'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/lib/unicorn/http_server.rb:529:in `spawn_missing_workers'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/lib/unicorn/http_server.rb:540:in `maintain_worker_count'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/lib/unicorn/http_server.rb:294:in `join'
from /usr/local/rvm/gems/ruby-2.1.3/gems/unicorn-4.9.0/bin/unicorn:126:in `<top (required)>'
from /usr/local/rvm/gems/ruby-2.1.3/bin/unicorn:23:in `load'
from /usr/local/rvm/gems/ruby-2.1.3/bin/unicorn:23:in `<main>'
from /usr/local/rvm/gems/ruby-2.0.0-p353/bin/ruby_executable_hooks:15:in `eval'
from /usr/local/rvm/gems/ruby-2.0.0-p353/bin/ruby_executable_hooks:15:in `<main>'
E, [2015-11-24T21:37:07.877451 #10157] ERROR -- : reaped #<Process::Status: pid 10627 exit 1> worker=0
I, [2015-11-24T21:37:07.877962 #10157]  INFO -- : worker=0 spawning...
I, [2015-11-24T21:37:07.880457 #10630]  INFO -- : worker=0 spawned pid=10630
I, [2015-11-24T21:37:07.889954 #10630]  INFO -- : Refreshing Gem list

I tried to update Gems, it didn’t work and I didn’t make any changes in source code.

Any help highly appreciated.