Auto Mask makes playback stutter / lag

Everytime I use auto-mask it makes playback of that section stutter. I tried doing original/optimized with Better performance, Better playback. I tried Proxy Preferred and created proxy media for the clip that has the automask on it. I also of course tried all of those options after hitting control R to render the section out. But every time I play back it stutters. I can use magnetic mask and it plays back fine. But sometimes the automask plug-in does a better job than magnetic mask, so I don't want to just NEVER use automask. 

Also as soon as I turn the automask plug-in OFF, for that clip, that section plays back fine. 

Any ideas how I can fix this?