Good to hear the bias solved some of the problems. As for the actual light leaks in the corners, I think they're caused by GI light leaking, which I presume is caused by either the current Voxel GI only bouncing once, or the fact that the actual GI voxels presumably are too big for smaller leakage areas such as the ones you show. I guess in the future the Voxel GI stuff could have some kind of adaptive thing, but I'm not really that much into that, I guess it's more Lubos's area.
A way to circumvent the problem is possibly adding shadowing buffer meshes (or something, I'm not sure what to call them). Basically, it's a sufficiently large box that shadows from the opposing side, like in the pictures below:
As for GI settings I think could be relevant might be the GI Step and GI Range, but I'm not exactly certain of the effects.
As for the saw pattern, my guess would be that either a bigger shadowmap (try 4K, 8K or 16K), or perhaps something with cascades not yet being supported by Voxel GI, or finally maybe it could be solved with soft shadows, although It's just what I can think of the top of my head