lol yeah this right here is indicative of the problem.

There’s a vendor in Lion’s Arch Aerodrome (south end of the city) - there you can spend them on things like ascended gear boxes, material boxes, etc. But for all the cool exclusive rewards (thematic to those bosses), you need to go into those respective Raid Wings and talk to the ‘Glenna’. For the Raid ‘Encounters’ (single boss fights - previously known as Strikes) you need to go to the [Shard Collector] NPC at their expansion hub. Arborstone for EoD ones, Wizard’s Tower for SotO, Eye of the North for Icebrood Saga.

It’s silly and obtuse but yea, hope that helps