Battery issues, low voltage on cell

Hello everyone, I’ve been flying for a bit on 5s batterys and it’s nice but I wanted something more casual so I picked up two 4s Tattu Rline version 2.0 batterys. Today when I went out to fly them both reported normal voltage’s on all cells on my buzzer. About a minute into the flight my buzzer started going off and my quad started descending even with increased throttle when I landed it I checked the buzzer and three out of the four cells read 3.7 volts but the fourth one read 1.1. This made me very concerned because I know that undercharged lipos are dangerous but there was no damage to the battery and it’s brand new also it wasn’t warm and it was balance charged previously the same day, I then flew the second battery and the SAME thing happened, this has me scratching my head… Do you think I have a battery with a dead cell, or is my charger broke? How should I go about this and if it’s a dead cell can I get a replacement as I ordered from race day quads. Thanks everyone.

to confirm battery good or bad use charger to balance charge. then check voltage of each cell with a multi-meter, if ok fly for a min or 2 and recheck voltage if all same (give or take a 10th )battery ok.
from what you are reporting sounds like batteries but BOTH seem strange if new.

When I plugged the lipos into my balance charger after the weird flight yesterday, they charged back to 15.2 volts in 10 minutes. That seems a bit quick. Thanks.