Double Axes and other similar heavy melee weapons (including the Unique variants in Arsenal (RPG Series) ) cannot disable shields. The weapons from RPG Series actually act like swords, as they can't destroy blocks in Creative Mode. Maybe the heavy melee weapons can act like the vanila axes? So that they can disable shields.
By the way, is the RPG Series being discontinued below 1.21?

Thank you for the suggestion.
I will consider this. Not exactly sure for which weapons.
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Due to the size of RPG Series it is only possible to maintain 1 game version at a time.