For comparison I did an endurance test on my 3x 4s 16Ah and yes, just below 3.6v under load they fall off the cliff really fast I was riding @ 43v then 500m later 42v... I limped home to about 41.6v at rest with these cell voltages;
3.44,3.45,3.47,3.53,3.45,3.61,3.64,3.41,3.40,3.37,3.46,3.37 -...