As shown in OpenRC's log: > /etc/init.d/metalog uses runscript, please convert to openrc-run.
Fixed via https://github.com/gentoo/gentoo/commit/adbb62f076f4867c6dcaad31db7e18ef1683175b#diff-783c2b45ba800dcb5d2497ac1349ca8e. You have to re-emerge the package to get the fix.