I e-mailed my poblem to access support and they answer me this...
My arp is working perfectly now
***Thank you for your mail. First off please make sure you're using an audio buffer
size between 128
and 512 in Logic's audio settings. Also set the processing buffer size to
"small" in the same settings
window.
Is it then still off? If so, is it still off even if you start the Logic
playback 1 bar ahead of the notes
triggering the arpeggiator?***
Thierry