Seplos BMS after disconnecting from active balancer.

I have been using a active balancer to setup battery cells. Connect to bms and 4amp balancer using the pack for a week to balance the cells. The balancer was set to start at 3.45v. when I they were 280 amp cells. After the week I could drain about 13kw from battery and it left it around 20% once the battery leads were disconnected and it running now. When a high load is on the battery it seems to drop the battery from 70% to zero I'm a minute.

What is going wrong???

Sounds like the BMS is shutting off for high current. What is the battery voltage before the bms? Also have you checked individual cell voltage?