1 hour ago, PatrickT said:I won't list Paul's recipe here, as I'm assuming that's a copyright violation - is that correct? I can provide details on that if it's helpful for problem solving.
It's generally considered that a list of ingredients can't be copyrighted so it's OK to share that. The text of recipe instructions can be subject to copyrights but paraphrasing, as you've done here is OK. Is this the recipe you are using?
A malt loaf is kind of an odd bird as it treads the line between cake and bread. Some recipes, like this one by Prue Leith doesn't even include yeast. I'm not familiar enough with it to offer much help except to say that that checking the temps of everything (water, proofing space, oven and baked loaf) is surely a good idea. And sinking is often a sign of underbaking.