This is an error related to the elasticsearch. The index is locked in read-only mode, you can unlock it using the Open Index API (https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-open-close.html).
This usually happens when there is not enough space left on the disk (when the disk is filled to 90% of its capacity). So before trying to use the ES API, take a look at your disk status
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