You will most likely want to use the MATLAB visualizations app to make a custom visualization.
One method would be to use the another field to write the error code. I am assuming the error comes from the sensor. If not you can also use MATLAB to pre process your data and find the mising data. (like here)
So assuming your sensor writes the errors, it can write using the same url above, but use of '&field5=myerror'
Now you can create a new MATLAB visualization from your channel view or from the pulldown apps menu.
Use thingSpeakRead to get the data fro your channel. (you can read the last few days of data or minutes, or just the last x number of points).
I'd aslo use 'outputformat' 'timetable' in the thingSpeakRead command. Then you can plot the time and the data points.
for example:
mydata=thingSpeakRead(<channelID>,'readkey','xxxxxxxxxxxxxxx','outputformat','timetable');
plot(mydata.timestamps,mydata.field1name);
text(mydata.timestamps,mydata.field5name);
I haven't tried that though. It might put NULL everywhere there is no data in field 2. Then you might have to do some extra filtering.
