When set up right both Android and iOS support huge data exchange fine (as it’s more and more frequent to see device firmwares update through BLE) - so i would suspect something wrong in the way you set up the connection.
Most disconnect with BLE I have seen come from issues with the connection parameters
A common one is the connection interval being too fast on the peripheral. mobile OS versions have varying minimums and Android does not agree with iOS leading to different behaviors.
From the top of my head I think that recent Android devices can support a connection interval as low as 7.5 ms, whereas iOS devices will expect at least 15ms.
There is also variation on the ability to exchange multiple packets during one interval where iOS and Android have different ways to handle that, so actual throughput is not just based on this minimum interval. (Basically there is a protocol to tell the other party you have more data to send and can do so within the same connection interval).
Older OS versions or hardware may have different capabilities as well, leading to possibly 30ms or more.
➜ I would deep dive into those parameters and may be use some sort of sniffer to see which side is issuing the disconnect.