Apparently this is an older bug, but I have a 310 Hereafter that I can't infuse into any weapon. It does appear on the "able to infuse list" next to my other higher light weapons, but the option to hold Square to dismantle isn't there, even if I get a beep when I press/hold it. None of my weapons are locked. I've tried switching characters, resetting my console, everything. Anyone got an idea?
Hereafter has a weird infuse bar. Since its description is longer than most weapons, it's infuse bar is pushed out of the visible screen. Bungie is completely aware of this issue and are working to shorten the description.
In any case, Hereafter is still able to be infused.
Try holding the infuse button for 15-30 seconds and it should infuse.