Attempting to run “classify ground” inside fence on loaded points results in zero ground points classified all the time.
Probable Resolution #1:
Ensure the settings option selected in the Classify Ground routine is not using “current ground points only” as your seed points if there are no existing ground points within the fence, otherwise no initial TIN will form and no points will be classified to ground.
Probable Resolution #2:
Verify the fence is large enough compared to the max building size such that a minimum of three points will be made ground. That allows an initial surface to be generated inside the fence and additional classification can then proceed using your classification maximums.