I apologize by the problems, but there is a large difference between Forest 3.9 and 4.0 regarding the Octane support:
in Forest 3.9 there was not Octane support at all, in fact the plugin just generates a mesh that is rendered by Octane. This mode is suitable for billboards, because the resulting mesh is not too big. Instead, this method doesn't work with 3D plants, because the geometry generated would be huge.
In Forest 4 we have included instancing support for Octane, that allows to rendering many high-poly objects with minimal memory requirements (basically it only keep a copy of each plant). This rendering method is very basic at this point, and some features would not work (for example billboards or Forest Color). We are working with Otoy to improve it, and should be improved in next releases (both of Forest and Octane).
Anyway, there is quick mode to put back the old method, and solve your problem: just switch "Display->Render->Mode" from "Automatic" to "Meshes" for each Forest object. This option disables the instancing support, and generates an unique mesh for Forest.
Regarding the software checking, we work hard checking our plugins before releasing a stable version (in fact, Forest 4 was available as beta for Pro customers for more than two months), but unfortunately it is not possible to test all possible combinations. Currently we support 14 Max versions (including 32 and 64 bit), all VRay releases from 1.5 to 2.4 (also 32 and 64 bit), 6 rendering engines (each one with their own versions), several modes of distributed rendering, and all of these using billboards, meshes, proxies... well, put all togheter and you can get an idea. But of course we are willing to provide quick support and fix all problems that may appear.
About the batch render, unfortunately this render mode is very problematic with the "Camera->Auto assign to active view" feature, because Max doesn't trigger a specific notification that we use to change the camera. When possible we encourage to use Backburner instead. Anyway, please give me details about the problem: do you use it with Octane or other engine ?