In my channel, there are several fields that their names was written with Unicode character -- '온도', '습도', '기압', ...
(FYI, 온도 is temperature, 습도 is humidity, and 기압 is air pressure)
It looks like thingSpeakRead function doesn't work well with non-ASCII characters.
The function reads '온도' field, but it throws Unrecognized variable name 'x' Error when it reads '습도' field.
However '습도' field is read since I renamed the field to humidity.