(The digital world is growing)
Just want to emphasize(!): if you have some redrawing issues with complex sessions - this could be a video card driver issue (not Ardour or Calf).
In the next following video Adrour and Calf plugins look well. (KX Studio 14.04.5, GeForce GTX 550 Ti, NVIDIA Driver Version: 384.90, (cuda-repo-ubuntu1404-7-5-local_7.5-18_amd64.deb)):
But in previous video:
vimeo.com/243397157 - there’s no cuda driver installed (AVLinux2017.4.9 RT-kernel have some problem with CUDA installation), that’s why there are some redrawing issues.