A performance optimization in Elastic Agent 9.3.4 causes timestamp fields sent from Beats based inputs and integrations to be incorrectly serialized to an empty {} JSON object. This does not affect the primary @timestamp field, only other timestamps fields in the event body.
This can lead to documents not being indexed at all (dropped or ending up in the failure store), or indexed with missing time fields.
The problem was already added to the release notes as known issue here.
The website has been updated, removing the download link from Elastic Agent 9.3.4 | Elastic with a description of the problem and its symptoms.
The binaries and images are still available for download.
The recommendation is to upgrade directly to 9.3.5 or more recent.