This is hard to diagnose from a distance. It probably has more to do with the server set up on the two WW servers than with WeBWorK itself.
Look for differences in the webwork2/conf/site.conf files -- you may be using lighttpd server instead of apache for images on one of them.
Check the apache log files looking for errors.
Using the web inspector (the exact name depends on the browser) in your
browser and look at the network time to see what files are being requested and how fast they are returning.
That's the most in the way of ideas that I can offer at the moment. Let us know what you find.