During Ruby and Rails upgrade Bundler showing dependency error

please help me here, I was upgrading ruby and rails and also dependent gems need upgrades.

Earlier the ruby version was 2.3.0 and rails was 4.2.x, now upgrading to 2.6.0 and rails to 6.0.4

If you see below error, actionpack is resolved to 6.0.4 and public_activity also needs actionpack >=3.0.0 which means 6.0.4 should be acceptable and obviously rails using version = 6.0.4, So why its an error. can some expert throw some knowledge on it.

Bundler could not find compatible versions for gem "actionpack":
  In Gemfile:
    actionpack (~> 6.0, >= 6.0.4)

    public_activity (~> 1.6, >= 1.6.4) was resolved to 1.6.4, which depends on
      actionpack (>= 3.0.0)

    rails (= 6.0.4) was resolved to 6.0.4, which depends on
      actionpack (= 6.0.4)

Bundler could not find compatible versions for gem "activemodel":
  In Gemfile:
    activemodel (~> 6.0, >= 6.0.4)

    active_model_otp was resolved to 1.2.0, which depends on
      activemodel

    paperclip (~> 6.1) was resolved to 6.1.0, which depends on
      activemodel (>= 4.2.0)

    rails (= 6.0.4) was resolved to 6.0.4, which depends on
      activemodel (= 6.0.4)

Bundler could not find compatible versions for gem "activesupport":
  In Gemfile:
    activesupport (~> 6.0, >= 6.0.4)

    delayed_job (~> 4.1, >= 4.1.9) was resolved to 4.1.9, which depends on
      activesupport (>= 3.0, < 6.2)

    factory_girl_rails (= 4.2.1) was resolved to 4.2.1, which depends on
      factory_girl (~> 4.2.0) was resolved to 4.2.0, which depends on
        activesupport (>= 3.0.0)

    jbuilder (~> 2.10) was resolved to 2.11.2, which depends on
      activesupport (>= 5.0.0)

    paperclip (~> 6.1) was resolved to 6.1.0, which depends on
      activesupport (>= 4.2.0)

    rails (= 6.0.4) was resolved to 6.0.4, which depends on
      activesupport (= 6.0.4)

Bundler could not find compatible versions for gem "capybara":
  In Gemfile:
    capybara (= 2.1.0)

    cucumber-rails (= 1.4.0) was resolved to 1.4.0, which depends on
      capybara (>= 1.1.2)

Bundler could not find compatible versions for gem "rack":
  In Gemfile:
    rails (= 6.0.4) was resolved to 6.0.4, which depends on
      actionpack (= 6.0.4) was resolved to 6.0.4, which depends on
        rack (~> 2.0, >= 2.0.8)

    sprockets (= 2.11.0) was resolved to 2.11.0, which depends on
      rack (~> 1.0)

Bundler could not find compatible versions for gem "rails":
  In Gemfile:
    rails (= 6.0.4)

    cucumber-rails (= 1.4.0) was resolved to 1.4.0, which depends on
      rails (>= 3.0.0)

Bundler could not find compatible versions for gem "railties":
  In Gemfile:
    coffee-rails (~> 5.0) was resolved to 5.0.0, which depends on
      railties (>= 5.2.0)

    devise was resolved to 4.8.0, which depends on
      railties (>= 4.1)

    doorkeeper (= 4.2.5) was resolved to 4.2.5, which depends on
      railties (>= 4.2)

    factory_girl_rails (= 4.2.1) was resolved to 4.2.1, which depends on
      railties (>= 3.0.0)

    rails (= 6.0.4) was resolved to 6.0.4, which depends on
      railties (= 6.0.4)

Bundler could not find compatible versions for gem "rotp":
  In Gemfile:
    rotp (~> 3.3.0)

    active_model_otp was resolved to 1.2.0, which depends on
      rotp

Bundler could not find compatible versions for gem "will_paginate":
  In Gemfile:
    will_paginate (= 3.0.5)

    bootstrap-will_paginate (= 0.0.10) was resolved to 0.0.10, which depends on
      will_paginate

I'm answering my own question, Since It got resolved after several iterations.

I removed Gemfile.lock and in Gemfile I start entering Gems one by one and then run bundle install each time, then eventually this problem did not occur.