Trouble installing ElasticSearch on Omeka 2.6

I succeeded in installing ElasticSearch plugin on Omeka 2.5, but impossible to get it working with 2.6.

– when I clear/reindex the database, there’s a status “in progres”, but no “completed” (the same after 1 hour, but my database is nearly empty…)

– when I type a search in the public page, I get this error :
Fatal error : Uncaught Error: Class ‘Elasticsearch\ClientBuilder’ not found in …omeka2/plugins/Elasticsearch/libraries/Elasticsearch/Client.php:26

So I copied ClientBuilder.php (in folder vendor/…elasticsearch/src) and added “require ‘ClientBuilder.php’;”, and the error message changes (another file not found).

Has anyone installed ElasticSearch successfully on Omeka 2.6 ? Do you have any clue to solve this problem ?
Many thanks in advance

EDIT : my install is on a Debian 9.7 OS, with PHP 7 and Apache/2.4.25 + elasticsearch-7.2.0

Actually it seems that the problem comes from another plugin that I had tried to install (AvantSearch).

I installed ElasticSearch on a brand new omeka 2.6 and it looks fine.

Previously, I had a problem with AvantSearch : I had this error : Call to undefined method AvantCommon::queryStringArg() …

So I assume something went wrong when uninstalling AvantSearch ?

Question : should I create another topic about AvantSearch ?

I think I’ve found the origin of the problem : I had an older version of AvantCommon (this plugin is required for AvantSearch).

I replaced it with the github version : and it works fine now.