ElasticSearch Index: Error: An index is already occurring. Try again later.

If you receive the error ElasticSearch Index: Error: An index is already occurring. Try again later. when performing an ElasticSearch reindex, it's possible the indexing flag for an in-progress index has got stuck. The resulting error will occur:

Error: An index is already occurring. Try again later.

In such a case, you can clear the flag by running the following:

wp elasticpress clear-sync 

Alternatively, if the above doesn't resolve the issue, it can also be stuck in a WordPress pransient. If so, you can try the following:

wp transient delete ep_wpcli_sync --network

Occasionally this value can also be stored in the object cache. Flushing the object cache should be performed with caution when working on live environments. You can flush your object cache via a new CLI Session, see: https://docs.altis-dxp.com/cloud/dashboard/cli/ and run the following:

wp cache flush

Note that flushing the object cache can have a significant impact on performance, so we recommend you only do this when necessary.