This Assets mod does something to the "Dinner" item and possibly others such as "Dwarven Stew" that removes their duration and makes them dissipate immediately when eaten.

I set all my characters back to standard looks and turned off this mod, and the dinner regained its duration, so I know it's this.

the mod is still invisible. is there a way to fix?

Game doesnt see that mod. Its not visible in game mod menu and in mod manager.