You need to make a selection of 12 ninjas even if you only use 4.
Since you only chose 7, the game system thinks that the 5 that you did not choose are actually defeated. That's why you could claim the "maximum of 6" one but not the "maximum of 3 or 1". Just choose another 5 more tomorrow and you're gold. Since these 3 can only be claimed once throughout the event, no harm done.
*PS. I find it annoying with regards to this system of the game detecting unselected ninjas as defeated because like you, I only use 4. :curse: