Thanks for your reply.
The TeX filter works fine with PNG output but not with SVG although with previous version of Moodle (3.6 I think) it was OK.
I don't understand why. You know Moodle uses the dvisvgm command with the PNG files previous genereted but there is no output with my server, even by hand when I do this command with CLI.
I though my PNG was not OK so I tried the same PNG file with my personal computer which as the MikTeX distribution and his own dvisvgm script : no bug !
So what ?