How to deal with light leaks?
I've also spent a good amount of time thinking about a solution for this problem. It seems like one those fundamental mismatches of taking a sparser, lower frequency structure (probe mesh, even if augmented with depth map) and lighting surfaces per pixel which themselves are occluders.

If you look at the SIGGRAPH'17 Precomputed lighting in CoD:IW (http://advances.realtimerendering.com/s2017/index.html) you'll see they partitioned the precomputed lighting into light maps for large surfaces (which have lots of occlusion) and using a probe mesh for small static objects as well as characters. They take a similar approach of storing an occlusion depth map per tetrahedra face, however because they're not lighting the occluders with the probe mesh, the discontinuities introduced are likely not noticeable.

Trying to light the occluders with the same map is extremely tricky because the probe mesh faces may not align well with the occluders. I.e. literally "corner" case where 3 planes meet doesn't encode well into a depth map. I have feeling they still get light leaks, but their density is probably fairly high and their evaluation points are distant enough from the pathologically bad cases.

Sometimes it might be worth asking level artists to not make single sided meshes or thin walls XD, at least for the time being.

Best of luck, if you find a robust solution to this, you should submit a paper to a conference and be graphics industry famous :D