This version contains a regression in multi_match queries that use the cross_fields scoring type. Elasticsearch

When running a multi_match query with the cross_fields type, Elasticsearch can sometimes throw an IllegalArgument exception with the message "totalTermFreq must be at least docFreq". If you use the cross_fields scoring type, it is recommended that you skip version 8.4.2. This regression was fixed in version 8.4.3.

Machine learning datafeeds cannot be listed if any are not modified since version 6.x

If you have a datafeed that was created in version 5.x or 6.x and has not been updated since 7.0, it is not possible to list datafeeds in 8.4 and 8.5. This means that anomaly detection jobs cannot be managed using Kibana. This issue is fixed in 8.6.0.

If you upgrade to 8.4 or 8.5 with such a datafeed, you need to work around the problem by updating each datafeed’s authorization information using these steps.

Orchestrators which use a settings.json file to configure Elasticsearch may encounter deadlocks during master elections (issue: #92812)

To resolve the deadlock, remove the settings.json file and restart the affected node.