I believe I have found the mod causing the problem, but it's not simply breaking the recipes: it's quietly changing the material requirements, notably to require significant amounts of Charcoal. It's the Woodcutter mod:
I didn't see this documented, so I was blindsided. It's not necessarily an unrealistic or unreasonable change, but it's certainly different, and quite unexpected when he fails to document what he's done.
The way that I found the change, with the tip from IsharaMeradin, was to expand Skyrim.esm in xEdit and look at the "Constructible Objects, which included the ingot recipes in question.
Now I need to decide whether I find this change appropriate, and if not then decide whether to try editing-out these recipe changes - I've never attempted anything like that - or just discontinue use of the mod. I had only added it provisionally day before yesterday and confirmed that I could indeed fell trees. (Sadly it doesn't achieve the primary goal I had in mind, which was being able to lumberjack my own logs for Hearthfire houses. This mod instead produces entirely unique lumber items for its own custom construction process using Jaxonz Positioner.)