Firstly, when i got these cells, i put them in series and charged them. I was surprised that the cell 1 triggered BMS on 3.65v when the 3 others were 3.43v.Although you don't have a picture to prove 3.62V each.
Presumably there was some divergence in voltages as shown down around 3.1V?
It seems like cell #1 has only 50% of expected capacity, but make sure cells really are top-balanced.
Sometimes after the act of parallel top balance people report settling to unequal voltage (happened due to poor contact), can't be sure at the voltages you show.
Some people report capacity a bit below spec on new cells, but nothing like 50%. It isn't badly bulged or some obvious difference, is it?
Oh, discharge rate: When cell hit 2.5V, how much current was being drawn? Contact resistance causes voltage drop below actual cell voltage. But that often shows up as elevated voltage on adjacent cell, so less likely.
Double check all cells with DMM.
So i charged them separately to 3.62v (not in parallel), didn't dismantle series. Cell1 was 99% already full. All the 3 cells took about 50Ah (5 hours charging with 10A per cell). Finally, every cells had same voltage and normally the same capacity.
6 hours later, i put a load, small load of 3.5A. About 13 hours later, BMS triggered on cell 1 at 2.5v when the others were 3.26v
There is no bulging, no difference.