FTP timeout : sticky connection issue ?

[oasis_ck]

Hey everyone,
We put in prod firewall pfsense with 2 WAN.
192.168.52.4 = WAN1
192.168.53.4 = WAN2
Sticky connection is enabled.
Gateway group failover and loadbalancing works like a charm.
But some users complain timeout when download multiple files from FTP server on WAN.
I pfTop while downloading a dozen tiny files from one FTP server and I notice that : each time I have a time out, SRC changed. (last line)

I tried conservative mode + 3600s tracking source timeout but no luck.


When I download one big file from this FTP server, I got no prob.
Thanks for your help