Hello! I checked and I didn't find any issue with the ones i've tried in your list so far, I think you might be using the bundled RMMV setting configuration which is not supported in the RMMZ VisuStella dragonbones union plugin, which is why you are not being able to load them up, for RMMZ you will have to readjust the suggested settings zipped with these to fit into the VisuStella Dragonbones union plugin format ! in all cases the only thing which carries over from the bundled RMMV settings is the file name to use to setup the battler, e.g 'LivingArmor' , and also the Motion names , e.g 'Attack A' , aside from that both the battlers and the action sequences are configured very differently in RMMZ
Hope that helps!