See https://forum-en.gw2archive.eu/forum/livingworld/dragonbash/Every-Piece-Matters-Bugged/. Plenty of the same complaint, no effective work-around posted.
I am stymied. Guess it’s time to give the dragon stuff a rest.
EDIT
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The work-around is to look in your inventory, find and destroy the kit, and then restart the event.
(edited by Obed.7629)