I've been looking into bug affecting elastic2045 with @dcausse where Elastic failed to start since /var/run/elasticsearch isn't present.
The elasticsearch-oss Debian package declares /var/run/elasticsearch in the package (via .dirs), and also ships a tmpfiles config in /usr/lib/tmpfiles.d/elasticsearch.conf
Looking at "systemd-analyze critical-chain" systemd-tmpfiles-setup.service was correctly started and there are also no errors in the journal for it.
Running "systemd-tmpfiles --create" correctly brought up /var/run/elasticsearch.
The next time this error happens, we should check whether the lack of the run dir is specific to elasticsearch or whether other directories declared in /usr/lib/tmpfiles.d are also affected.