Apparently Gerrit Trigger is always generating build urls (<BUILDURL> paremeter in its config) that do point to the good old but deprecated BUILD_URL.
Blue ocean URLs are exposed inside job via the RUN_DISPLAY_URL variables.
Plugin should allow user to configure which urls to use.
Ideally it should be a global option that will tell the plugin to use one or another URL, so we would not have to update all comments.
It appears that the default "BUILDS_STATS" variable content is not customised and that is the one that should contain (or be allowed to contain) the new URLs.