My guess is that you connected your GND and GNDD nets somewhere on the schematic. If you want both names to continue to exist then you need to use a net tie. (My guess would be that you want separate ground planes if this is the case. *) If not then only use one of these labels.
More details see regarding how kicad chooses a net name if multiple labels are on the same net: Other net used in PCBnew than indicated in EEschema
*) Using separate zones is not always the best idea. In a lot of cases it is better to have an uninterrupted ground plane on an inside layer. If you have separated zones then make sure that you never cross that separation with a trace as you would then create a slot antenna. (Solution is to place a capacitor right nest to the trace to bridge the gab for high frequency parts of the return currents.)