Insights Clients are no longer checking in after upgrading the satellite to 6.9 version

Issue

• After upgrading Satellite to 6.9, servers registered via insights are no longer checking in.
  This issue is also observed on new insights-client registered to Satellite 6.9
• All the clients are no longer checking in to insights after upgrading the satellite to 6.9 which is behind a proxy server.

• Insights client registration failing with error Upload status: 500 Internal Server Error

  2021-05-07 15:54:58,662  NETWORK insights.client.connection POST https://satellite_URL:443/redhat_access/r/insights/uploads/xx-xx-xx-xx
  2021-05-07 15:55:58,764  NETWORK insights.client.connection Upload status: 500 Internal Server Error {
  "error": {"message":"Timed out connecting to server"}
  }
  
  2021-05-07 15:55:58,765    ERROR insights.client.connection Upload archive failed with status code  500
  2021-05-07 15:55:58,765    ERROR insights.client.client Upload attempt 1 of 1 failed! Status Code: 500
  2021-05-07 15:55:58,765    ERROR insights.client.client All attempts to upload have failed!
  2021-05-07 15:55:58,765    ERROR insights.client.client Please see /var/log/insights-client/insights-client.log for additional information
  2021-05-07 15:55:58,765    ERROR insights.client.phase.v1 Upload failed.
  

• Satellite Web UI not responding or slow because all insights connections are stuck and timed out after 60 seconds as below.

  # production.log
  2021-06-13T09:35:54 [I|app|9ccc8b5f] Started GET "/redhat_access/r/insights/v1/systems/XXXX-XXXX-XXXX-XXXXXXX" for XX.XX.XX.XX
  2021-06-13T09:35:54 [I|app|9ccc8b5f] Processing by InsightsCloud::Api::MachineTelemetriesController#forward_request as JSON
  2021-06-13T09:35:54 [I|app|9ccc8b5f]   Parameters: {"path"=>"v1/systems/XXXX-XXXX-XXXX-XXXXXXX"}
  2021-06-13T09:36:54 [W|app|9ccc8b5f] Action failed
  2021-06-13T09:36:54 [I|app|9ccc8b5f] Backtrace for 'Action failed' error (RestClient::Exceptions::OpenTimeout): Timed out connecting to server
  2021-06-13T09:36:54 [I|app|9ccc8b5f] Completed 500 Internal Server Error in 60480ms (Views: 10.9ms | ActiveRecord: 2.4ms | Allocations: 1088649 <====