Index creation does not work

I'm trying to create an index from Kibana since I already have logs in elasitcsearch.

If I go to Stack Management > Index ptterns, give it an index pattern name, and then run Create index pattern, I am taken to a page stating that the index has been created. You can check the type of Fields here.

However, when I open Discover, the page to create the index pattern is displayed and I cannot check the index.

What should I do?

elasticsearch is not outputting any significant logs.

The kibana log looks like this

# tail /var/log/kibana/kibana.log
... snip ...
{"type":"log","@timestamp":"2021-04-07T13:05:55+09:00","tags":["warning","plugins","monitoring","monitoring","kibana-monitoring"],"pid":25076,"message":"Error: Cluster client cannot be used after it has been closed.\n    at LegacyClusterClient.assertIsNotClosed (/usr/share/kibana/src/core/server/elasticsearch/legacy/cluster_client.js:195:13)\n    at LegacyClusterClient.callAsInternalUser (/usr/share/kibana/src/core/server/elasticsearch/legacy/cluster_client.js:115:12)\n    at sendBulkPayload (/usr/share/kibana/x-pack/plugins/monitoring/server/kibana_monitoring/lib/send_bulk_payload.js:22:18)\n    at BulkUploader._onPayload (/usr/share/kibana/x-pack/plugins/monitoring/server/kibana_monitoring/bulk_uploader.js:209:43)\n    at BulkUploader._fetchAndUpload (/usr/share/kibana/x-pack/plugins/monitoring/server/kibana_monitoring/bulk_uploader.js:195:20)\n    at runMicrotasks (<anonymous>)\n    at processTicksAndRejections (internal/process/task_queues.js:93:5)"}
{"type":"log","@timestamp":"2021-04-07T13:05:55+09:00","tags":["warning","plugins","monitoring","monitoring","kibana-monitoring"],"pid":25076,"message":"Unable to bulk upload the stats payload to the local cluster"}

It seems that the index is indeed being created.

GET /_cat/indices?v
health status index                                uuid                   pri rep docs.count docs.deleted store.size pri.store.size
yellow open   api-2021.04.07                       7Ng-eUJ-Ty-1CsM068iJqg   1   1     738980            0    120.9mb        120.9mb

Why does Kibana refuse to create index patterns?

It might be affected by the change in the destination of elasticsearch's index.

I restarted kibana and now I can create the index pattern.

systemctl restart kibana.service

However, after restarting, there were many index patterns that kept being created, mistakenly thinking that they had not been created before.

Hi
Which version of Kibana are you using and in which environment?
Thanks & Best,
Matthias

Thank you for your comments.
I am using Kibana 7.12 (latest) on CentOS 7.

Thx, do you use a proxy in your setup?

Yes, it is.
For security reasons, the internal network is connected to the external network via a proxy server.