I didn't know this limitation on Rebus Farm...
Forest adds some hidden meshes in the scene, which are used for the billboards. They are scaled to zero size, and placed in the layer "_forest_templates". Some of them are animated (as the _forest_template_Low Animated Plane).
You cannot delete these objects (because they are recreated), but you cannot remove their keyframes if needed. Use select by name to pick them.
I'm not sure if this would be the problem, because i see other objects in the log. Anyways, aside from these templates, Forest doesn't add other keyframes in any way.