Red Hat Satellite 6 repository sync failed with PLP0000: not well-formed (invalid token)

Issue

• Red Hat Satellite 6 repository sync failed with PLP0000: not well-formed (invalid token):

  2020-04-28T12:08:18 [I|app|] Current user set to testuser (admin)
  2020-04-28T12:08:18 [E|bac|] PLP0000: not well-formed (invalid token): line 156, column 200 (Katello::Errors::PulpError)
  /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.10.0.59/app/lib/actions/pulp/abstract_async_task.rb:122:in `block in external_task='
  /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.10.0.59/app/lib/actions/pulp/abstract_async_task.rb:120:in `each'
  /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.10.0.59/app/lib/actions/pulp/abstract_async_task.rb:120:in `external_task='
  /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.10.0.59/app/lib/actions/pulp/repository/sync.rb:34:in `external_task='
  /opt/theforeman/tfm/root/usr/share/gems/gems/dynflow-1.1.6.1/lib/dynflow/action/polling.rb:98:in `poll_external_task_with_rescue'
  /opt/theforeman/tfm/root/usr/share/gems/gems/dynflow-1.1.6.1/lib/dynflow/action/polling.rb:21:in `run'