Copying answer from comment, with some additional tests. My results are in the comments. Note that using Default, ASCII or UTF8 does work on my machine - it also should on yours.
// returned from www.bytes, copied here for readability
byte[] bytes=new byte[]{116, 101, 120, 116, 105, 110, 101, 115, 115};
string customDecoded="";
foreach(var b in bytes)
customDecoded+=(char)b;
Debug.Log(customDecoded); // textiness
Debug.Log(System.Text.Encoding.Default); // System.Text.ASCIIEncoding
Debug.Log(System.Text.Encoding.Default.GetString(bytes)); // textiness
Debug.Log(System.Text.Encoding.ASCII.GetString(bytes)); // textiness
Debug.Log(System.Text.Encoding.Unicode.GetString(bytes)); // 整瑸湩獥
Debug.Log(System.Text.Encoding.UTF7.GetString(bytes)); // textiness
Debug.Log(System.Text.Encoding.UTF8.GetString(bytes)); // textiness
Debug.Log(System.Text.Encoding.UTF32.GetString(bytes)); // 整湩
Debug.Log(System.Text.Encoding.BigEndianUnicode.GetString(bytes)); // 瑥硴楮敳
Please check if System.Text.Encoding.Default
is ASCIIEncoding, maybe something changed the default value?