Ok, it's working now on a self hosted version of Flowise and a cloud version of Arize. I have updated to the last version of Flowise docker's (5 days since my last updated, a while in the AI area ah ah)
Okey, the issue is from my side. Using the flowise official website, I have the traces. Using a self hosted version of flowise, I don't have any trace. I'll investigate it