I agree with Neil that it appears to be scale related. If it appears readable at 1:3k, when at 1:657k+ it's not going to be usable anyway, so maybe
1) you gave it cached but not at 1:657k As a scale level plus, OR
2) you have it as a scale factor but not cached at the scale and on-demand turned off. OR
And more likely...
3) the source Layer in the mxd used to created the service is using scale depend drawing and has that Layer turned off at that scale. Again, the display at the 1:657k scale would be so dense it would be useful, so typically you would turn that off at that scale in the source mxd feeding the service, and/or use something like symbol representation to simplify the lines as you zoom out, maybe simplified to display neighborhoods boundaries v's plots....city boundaries v's neighborhoods, etc. as you zoom out. Drawing would be faster and more useful at those scales.