Grey arrows in weathermap?
What does your scale look like?
Weathermap doesn't show anything as up or down - it just takes a number and turns it into a colour. If the scale (which does the translation) has gaps, or is incorrect for your interpretation
of the data, then you might get grey arrows. The most common problem like this is where people have a scale like
SCALE myscale 0 1 255 0 0
SCALE myscale 1 2 0 255 0
SCALE myscale 1 1 255 0 0
SCALE myscale 2 2 0 255 0
and then get a value of 1.5. If you are storing things like interface status in rrd files, then you sometimes get values in between 1 and 2, even if you think that you can only get 1 or 2 back from the device, depending on how you have set up the rrd parameters. It will produce an average if those aren't correct.
The easiest fix is:
SCALE myscale 0.5 1.5 255 0 0
SCALE myscale 1.5 2.5 0 255 0
Now there are no gaps. The actual state might still be wrong though - if the average is 1.7 because the state has only recently changed from 2 to 1, the map will show an incorrect state. So the real answer is to fix the rrd parameters if this is what the problem is.