The nokogumbo gem has been a dependency on many Rails apps as part of using sanitizer, which helps on dealing with HTML input/output.
Because nokogumbo relies on natively-compiled modules, it's sometimes tricky to have it properly deployed on EYCloud.
For Stack v5, it is advised to add the following lines as part of the 'before_bundle.rb' deploy hook:
# Install Nokogumbo gem with special flags run 'bundle config --local build.nokogumbo --with-ldflags=-Wl,--undefined'
On Stack v6 the above code is no longer needed.
As always, your mileage may vary. Do open a ticket with EY Support in case the above still doesn't solve issues when deploying an app that requires nokogumbo.