I had an issue in Sugar where some custom modules refused to appear in the Global Search settings, meaning I couldn't index them in ElasticSearch.
When I checked the module oddly enough unified search would be enabled:
1. Re-enable the module
To force it to be re-enabled update/create this file
and add this setting.
$dictionary['<MODULE>']['unified_search'] = true;
2. Re-enable a field
You'll also need a field using the unified index before SugarCRM
Enable unfied_search as a setting.
After a quick repair/rebuild. My module appears in the Global Search Settings and I can poll it as normal through ElasticSearch.