Yesterday i tried to infuse my 335 hereafter into my Conspiracy Theory-D. And it also showed up in the menu to infuse but when i clicked on it i just got a weird noise i checked if it is locked it was not. I also tried to equip and unequip it nothing worked. I would like to know why.
You may want to hold down X/Square longer to infuse this weapon. As an exotic weapon, it takes a bit longer to infuse the weapon into another (around 7 seconds).
You may not be able to see the progress bar for infusing, due to the weapon tooltip. That i an issue Bungie is aware of as stated here: https://www.bungie.net/7_The-weapon-tooltip-in-the-Infusion-menu-can-be-par/en/Help/Article/13960