J'ai eu quelques échange avec le support ubiquiti, des tests avec iperf3, des updates vers version beta, : 
pour conclure : 
Thank you for your patience. 
 
I discussed these case details with the internal team, we are getting a slow data transfer rate while the traffic is routing through the L3 network. 
In this case, threat management will also affect the data transfer rate ( the inter-VLAN traffic is included in the threat management scanning). 
 
To achieve higher inter-VLAN throughput we will recommend to upgrading the console to UDM Pro/ UDM SE (high processing and performance consoles) or connecting L3 switches in the network. 
Best,
UI Support
Ubiquiti Inc.
Bref, je repasse le nas dans meme vlan que mes pc