Why is azure file share openReadAsync() breaks when file over 4mb?

Question

I'm trying to openReadAsync() csv file from azure file share. But if the file is over 4mb ReadLineAsync() returns whole file as [���������������������������], instead of returning first line.

Here is the code i use to create stream

var dir = GetCloudDirectory(type, isImport);
var cloudFile = dir.GetFileClient(fileName);
var stream = await cloudFile.OpenReadAsync();
var reader = new StreamReader(stream);
var firstLine = await reader.ReadLineAsync();

Any ideas how to debug this or what could be the problem?