Actually it seems they updated the security announcement to explicitely cover this new vulnerability:
[Update 15 December] A further vulnerability (CVE-2021-45046) was disclosed on December 14th after it was found that the fix to address CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. Our guidance for Elasticsearch, APM Java Agent, and Logstash are unchanged by this new vulnerability.