HTML5 post process seemingly not functional?

Hey all,
I’ve just started work on a side project that requires outputting as HTML5, so I’ve gone back to UE4.22.3 for this project (because i had it installed).
I’ve created an edge-detection post processing material that works just fine in the editor, however it barely shows a few pixels in the packaged HTML5 output.

In the editor it looks like this:

However, in the HTML5 output the same scene looks like this:

The material function i’m using for this looks like:

(This goes into the B of the LERP node in the last image)

(This is the alpha for the LERP node in the last image)

(the pin going off the bottom middle here goes to an unused node, so i didn’t screenshot it)

Any help with this would be greatly appreciated, thanks in advance!