Logstash crashing - Spawning new process every few seconds

I have logstash v5.0.1 running in Redhat Enterprise v6.8. Recently, I tried to install plugin "logstash-output-email" using command-line from Internet using below commands.
wget https://api.rubygems.org/latest_specs.4.8.gz
And, extracted to logstash bin path and then executed below commands.
./logstash-plugin install logstash-output-email
/usr/share/logstash/bin/logstash-plugin install --no-verify logstash-output-email
But none of them worked due to proxy and it failed. Then I came to knew that proxy is not enabled due to security reasons. So I reverted the configuration in the output plugin and restarted the logstash service.
Then I noted logstash is spawning new process and process ids every few seconds and I see the below error messages appended to the /var/log/logstash-stderr.log file when logstash is running. Why is it still referring the Gem dependencies. It didn't install since there is no internet connectivity. so logstash should be running without issues, right?

Bundler::GemNotFound: Could not find gem 'logstash-output-email (>= 0) java' in any of the gem sources listed in your Gemfile or installed on this machine.
verify_gemfile_dependencies_are_found! at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/resolver.rb:328
each at org/jruby/RubyArray.java:1613
verify_gemfile_dependencies_are_found! at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/resolver.rb:307
start at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/resolver.rb:199
resolve at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/resolver.rb:182
resolve at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:192
specs at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:132
specs_for at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:177
requested_specs at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:166
requested_specs at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/environment.rb:18
setup at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/runtime.rb:13
setup at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler.rb:122
setup! at /usr/share/logstash/lib/bootstrap/bundler.rb:64
(root) at /usr/share/logstash/lib/bootstrap/environment.rb:64
Please help me with a solution how I can start the logstash without issues and starting working. Please suggest.

Start by reproducing the Logstash 5.0.1 startup failure and inspect /usr/share/logstash/lib/bootstrap/bundler.rb together with the Bundler resolver trace under vendor/bundle. Check how the failed logstash-output-email installation remains represented in the Gemfile or dependency state; done means Logstash starts without repeatedly spawning processes or reporting GemNotFound.

Written by the indexing model from the issue text.