I use Magix Movie Studio Platinum 13 (just a slightly pared down version compared to Vegas), and it's always had problems with Waves plugins. I can turn up the ASIO buffer size on my interface and it helps, but doesn't solve the problem completely. There's just some horrible inefficient use of the audio path when plugins are applied.
It's irritating as heck. Coupled with its total refusal to use GPU acceleration for rendering, I've about had it with this product line of software. I'm looking to move to another editing product but I can't find any other good ones that have VST support without using an external audio editor.