Three possibilities to check first...
The address of the odd fixture doesn't match the patch in the desk. Correct one or the other.
The odd fixture is working in a different mode to the others. Check and, if necessary, correct the odd fixture.
The odd fixture was in a different mode when the show was recorded but has been corrected since. Check the patch and, if necessary, correct the patch of the odd fixture.
Don't forget you can display and examine the desks DMX output to see if it is sending the same thing to all the fixtures but make sure you know what addresses the fixtures are actually set to. Don't rely on the patch or a paper record.