According to Augustine, a predication of an evil—say, the Sam is blind—is made true by a conjunction of two states of affairs. The first of these is a purely negative state of affairs, that the subject lacks a feature F. The second of these is a positive state of affairs, that the subject is of a sort that ought to exhibit F. Thus, Sam lacks sight but has the property of being of a sort that ought to exhibit sight.
If memory serves me (and if it doesn't, then it's still an interesting view), Augustine will then say this about Sam's blindness. Consider Sam*, a person much like Sam, except that he isn't of a sort that ought to have sight. Then, just like Sam, Sam* lacks sight. But Sam* also lacks the positive property of being of a sort that ought to exhibit sight. Therefore, Sam is better off than Sam*, despite the fact that Sam has an evil while Sam* does not. Now the problem of evil doesn't come up in regard to Sam* not having sight. And Sam is better off than Sam* in respect of sight, so why should it come up with regard to Sam?
Or let's put it differently. Take Sam*, and give him a new purely good property. How can Sam* become worse off simply by virtue of acquiring a new purely good property? Well, then, if we give Sam* the good property of being such that he ought to have sight, he doesn't become worse off. But then he's just like Sam. So the problem of evil shouldn't come up with regard to Sam.
Here's a problem with this reasoning. Suppose Sally believes that she lacks some very minor good G. Now, we give Sally the good G. By the above reasoning Sally should be better off. But perhaps not. For now Sally has a false belief that she previously didn't have. And the disvalue of that false belief may outweigh the minor good G.
However, we might distinguish between narrow and broad well-being. Things that do not causally interact with one or aren't intrinsic properties of one only belong to broad well-being. For instance, that my friends aren't saying bad things about me behind my back only contributes to my broad well-being. But that I am healthy is a part of my narrow well-being. So here is a suggestion. Now, narrowly, Sam* is narrowly no better and no worse off than Sam. And if Sally doesn't narrowly become worse off for being wrong about G. So maybe with regard to narrow well-being the principle that gaining a good by itself doesn't make one any worse off is true.
If this is right, then Augustine's arguments may work with regard to the problem of evil specialized to narrow ill-being. But that still leaves the problem of evil in the case of broad ill-being. However, maybe with the latter we may suppose that for all we know we really are very well off broadly speaking, because our broad well-being may include things very far beyond us.