We might be in a situation where we have inserted multiple times the same item which is problematic. The issue was spotted on one of our production instance on a artifact that has been moved.

Trace:

Adding artifacts to the index queue
  35/573 [=>--------------------------]   6%
In MeilisearchMetadataDAO.php line 43:
                                                                                   
  Do not expect to find more than one indexed item (plugin_artifact_field, [Array  
  (                                                                                
      [field_id] => 28349                                                          
      [artifact_id] => 102327                                                      
      [tracker_id] => 1083                                                         
  )                                                                                
  ])

This is not really easy to fix after the fact as it also requires to interact with the FTS backend. The easiest way to resolve it is:

1. Drop all the Meilisearch data if used
2. In the siteadministration uninstall then re-install the FTS plugin to clean its dataset