Issue capturing map boss using ritual vessel

I cleared the map boss before my last ritual, but at the last ritual when i used the vessel, the boss name does not appear in the vessel. I went to the boss room with the ritual and used a 2nd vessel, low and behold I managed to use the vessel, this time with the boss name. So I managed to use 2 vessels in 1 ritual encounter, and the boss only gets captured in the ritual where the boss was in.