Any engineer that holds a bundle and changes skills automatically drops the bundle. Not only that, but occasionally the bundle outright disappears or bugs out.
Notably, in the Swamp Fractal where you have to carry the wisp, swapping skills makes the wisp disappear.
In the Colossus Fractal, you cannot change skills without dropping your item.
Some specific events or consumables grant you a bundle that, upon switching skills, it automatically destroys the held bundle.
I understand that this coding is in place to prevent Engineers from being powerful and swapping skills after equipping a kit, but why are ALL bundles altogether dropped when an irrelevant skill is changed? It’s an unintended side-effect of the coding innate to the Engineer.