Your welcome! I was a wild guess, but I was thinking things would get pretty nutty without any height attribute for your divs
If anyone else runs into this in a future search and has to support an older browser, I think maybe you could do a relatively simple fix as a redundant fallback through the custom code CSS. I think if you also set the body as 100% and then also declared immediately after using VH, modern browsers would use the latter and older browsers would probably ignore VH and use the 100%. But you would have to rely on percentages for all other styles. It would be a lot of work in retrospect without a find and replace in your case, but a code export of the CSS would build a tight simple hitlist.