Actually, I don't think many people will notice about this but i hope this information works for everyone:
- The Claim rewards will be disappear in 10 minutes after the raid boss is cleared (0% HP)
- After you raid the boss, the rewards won't automatically go to your mail box, so you have to claim it manually to the treasure tab
- You can claim the chest rewards on the Boss that you have defeated, because the system automatically move to the next boss raid after you defeat it so that's why we didnt notice that the treasure tab is also change to the next boss (<< i dont know if everyone gets this or not)
I hope i make things clear , this information is provided by other friends too so I hope it can be helpful

will be disappear in 10 minutes?? I think it's "will be appear" meaning you can start claiming the rewards 10 min after boss is killed?
My guild cleared the boss last week and my bf still can claim it hours later O.o so I assumed it can be claimed until the reset...
did they change?
Anyway also agree that reward should be auto sent in the case that the guild kill boss near reset time and not everyone have a chance to claim it.