Try discharging the batteries completely first (e.g. connect a washing machine or electric oven) and then charge them to 100%. Possibly twice in succession. Do the same with an additional battery. The update must also be carried out a second time with an additional battery.

To the left of the power connection for charging is a slide switch called the "AC charging speed switch". When the switch is "up", it charges what is maximally possible. When the switch is "down", the limits of the EcoFlow app are used.

Hello
I forgot to ask if you have done the last update.
Best regards Viktor