ReadLineAsync returns Null

[THop]

Describe the bug
All lines read from files are null when build with --configuration Release

Code:
using var stream = await _fileReference.OpenReadAsync();
using var reader = new StreamReader(stream, Encoding.UTF8, true, 10000);
string line;
while ((line = await reader.ReadLineAsync()) != null)
{
yield return line;
}

line is always null when build with Release.

When building with Debug no problems occur.

[THop]

Sorry problem was at my end,
while ((line = await reader.ReadLineAsync()) != null)
this didn't work on release
i replaced it with

         var line = await reader.ReadLineAsync();
            while (line  != null)
            {
                var returnLine = line;
                line = await reader.ReadLineAsync();
                yield return returnLine;
                
            }

This did work