Convolution Kernel Find Edges alter cropping of my footage

Hi, when I apply the Convolution Kernel Find Edges effect, it looks the way I think it should- covers the entire image evenly as I want it to.  However, when I render my sequence, it awkwardly cuts or crops new edges on the footage, leaving weird awkward blackspace that doesn't match the edges of any of my other footage in the sequence.  See below for examples:

Before applying Convolution Kernel Find Edges:

After applying Convolution Kernel Find Edges but before rendering (very dark I know, sorry):

After rendering Convolution Kernel Find Edges:

I know it's probably really hard to see because it's pretty dark, but if you look along the bottom edge of the final shot you can see the footage I'm fading in from showing through clearly in a weird little wedge.  Not sure why it's doing this.  Any thoughts appreciated.