X265's latest changes broke the plugin again. This time, the rateTolerance field was removed from the public API. An option called bStrictCbr should be used instead if you need strict constant bitrate tolerance. See: https://bitbucket.org/multicoreware/x265/commits/ac94f35f450546c90bf46d431cc9d6651347fa2f
As per the recommendations in that changeset, rateTolerance is no longer available if your X265_BUILD >= 41. The second part of this patch is to add support for bStrictCbr, which becomes available if your X265_BUILD >= 41.
Apply the patch with "patch -p1 < rateToleranceV41.diff".
This patch has been tested up to the latest x265 trunk, and is working with X265_BUILD == 45.
Thanks mean, and let me know if you have any questions.