Not sure, but I think function play.api.mvc.Result#discardingCookies in Play 2.6.0-M3 works incorrect. It adds new discarded cookie, but doesn't removes old cookies.
For example before using discardingCookies I have single cookie:
Cookie(id,test-id,Some(43200),/,None,true,true,None)
After I discardingCookies have:
"Cookie(id,test-id,Some(43200),/,None,true,true,None)"
"Cookie(id,test-id,Some(43200),/,None,true,true,None)"
"Cookie(id,,Some(-86400),/,None,true,true,None)"
So they all have same names. Play 2.5 doesn't have that problem because it was using ListMap - so every cookie name was unique. Now it is just Sequence.
Should I write that to github issues?