This can be reproduced permanently by following steps:
1. Connect to a simple echo server endpoint
2. send 4+ messages length >10000.
3. Check the received message if they are the same with those sent.

It will show unexpected received duplicate message.
This can be reproduced by following sequence:
//for each all message
1. sendText(msg);
// after all send invoked
2. receive and check messages

But if try following steps, there is no such issue:
// for each all message
1. sendText once per message
2. receive/check before next sent

From captured network communication, there is a frame with duplicate data s. And that message is exactly the one failed during verification.
Please confirm if it is the problem.

I will attach test and captured data.