Besides checking your scene, i must add that Camera Limit not always improves the performance, specially with recent Max versions.
It depends of many factors, as the relation between the number total of items and removed by clipping, size of the distribution, etc.
Please note when Camera Limit is enabled, the Forest object must be rebuilt when camera moves.
Depending of the build time, that may be worse than displaying all items at viewport.
For this reason, in recent Forest versions, the plugin doesn't suggest to enable Camera Limit by default, as in older releases.
Depending of the scene, you should evaluate if this feature adds some benefit, or a performance hit.
By the way, to unlink Forest from the Camera completely, it's necessary to change all these parameters:
1) Turn off "Limit to Visibility".
2) Turn off "Auto assign to active view".
3) Click Camera->Clear, to remove the current Camera, if any.
I hope that helps.