Using Full-Text indexes on attachments with filters conversion not working on xSP server

I use the same database with some documents and .pdf, .txt attachments , when I index my database with options : index attachments with filters conversion.

On a standard server Domino 8.5.1, it’s working and I find documents with pdf or txt files.

On a xSP server Domino 8.5.1 (xSP environment), it’s NOT working only the documents with txt attachments are found.

Any idea for this problem ?

Thank you in advance.

Sylvie