Why has my cold smoking stopped working?
It sounds like you may be over-curing the fish. The salt and sugar draw water out of the fish, the longer it's applied the more is lost, and you can go too far. When I cold smoke a side of salmon it's only cured overnight, say 8-10 hours, not for a whole day.  I imagine there wouldn't be much left after that.
Try reducing your dry brining time to 4 hours, then rinse, pat dry and let them dry out overnight in the refrigerator.