You can do a 2nd test.
Run that sp from withing bids (data / query window).
You'll see if the results are getting returned correctly. Then you can do the same on the report server.
Once you know that is NOT the issue then you know that the rendering is the issue (too much code, groups, iifs, conditional formatting, etc).
1 option is to change the sp to return the least possible amount of data so that you have less rendering work.