My two cents.....
I also have one of these V2 units (my LV reg blew on first time I hooked it up, see earlier posts) and 20 yrs ago I got my BSEE. (I have long since been neutered by project management) From my semi professional viewpoint, I seriously doubt it is a 4 layer board, both from personal observation(not thick enough) and the cost/benefit analysis. 4 layer boards are much more expensive to produce than a board that is twice as large. It would make more $$ and sense to put two- 2 layer boards in one case, a fine one for digital logic and a beefy one for power xfer.
4 layer boards create much higher QC rejection and manufacturing costs, and are only used when absolutely necessary. QC is obviously already an afterthought, as they are shipping marginal units with 6 FETS in a design for 12, and with a 4 layer board, I doubt 1 out of every 4 they produce would work out of the box. (wait-perhaps that is about what we are experiencing?)
I believe Fechter is correct that the solder mask is covering the vias and many other traces that account for the missing connections.
Update: my v2 unit is out for warranty repair, and WILL be replaced with a 12 FET version, or I will reject it again!
Thanks for the help and support for someone who hasn't enjoyed their first mile of E-bike commuting. I am already planning a V2 build, even though I haven't finished V1.
I admire the engineering talent and user insight that shows up in this forum!