The logs indicate that Kibana's saved object migrations fail during the INIT step. In this step we make the following request to Elasticsearch: GET /.kibana,.kibana_7.13.4?ignore_unavailable=true and for some reason this request is reaching a timeout.
Could you try to manually test this with curl:
curl -X GET "elasticsearchUrl:port/.kibana,.kibana_7.13.4?ignore_unavailable=true"