I’ve made about 15 batches at this point...all have come out fine after bottle conditioning. Nothing amazing but well carbed and flavorful. But with a few of them there has emerged that buttery diacetyl off-flavor, BUT it has been several weeks down the line after bottle conditioning. In other words, for the first couple weeks after the beer has been carbed and ready for drinking, they tasted great. Then I would open one a week or two after that, and I sensed that buttery off-flavor. Why would it come on so late? Are the other flavors of the beer possibly dulling so now that is coming through? Does further bottle conditioning by the leftover yeast start to create that eventually? So odd.