elasticsearch_mappings.json is not installed if Elasticsearch support is compiled in. This is a regression in 4.16 and master.
Have patch, need bugnumber.
This bug was referenced in samba master:
Created attachment 17139 [details]
Patch for 4.16 cherry-picked from master
Pushed to autobuild-v4-16-test
This bug was referenced in samba v4-16-test:
This bug was referenced in samba v4-16-stable (Release samba-4.16.0rc2):