After creating a mask with feather, my clip disappears during playback. I have tried tracking the clip, adjusting the keyframes and a host of other possible issues, but the clip disappears. What am I doing wrong? ...or is this a glitch?

ZIP file attached. Let me know if you see the same issue. As I said, during playback, the background image disappears. I've tried changing the opacity and it has no effect. This is one of many sequences I am using. I plan on using this masking effect as much as possible throughout the video for background vignettes. All the sequences are going to be spliced together onto a main master clip. I sincerely appreciate your help with this.