My2cents: the cookie domain attribute is not correct: you would like .edf.fr so it’s valid for all sub domains but you didn’t provide an explicit domain so Gatling used the one from the baseUrl, eg foo.edf.fr
Well I edited my post to remove the exact domain but too late apparently haha
Following your post I’ve been messing with different options and it apparently worked, so thanks for the help 
Tho I haven’t reached the request that has been bothering me for quite some time now yet, so I might post again here soon