If you're simply loading up a save, odds are that Renpy didn't process the images with the shader yet. For some reason, a bunch of images before you save (and sometimes after) won't get hit. It can take up to a couple of minutes of gameplay before you hit the shader.
Also, it simply doesn't improve the look that much. It does a bit of denoising and sharpening, but it can't magically make the renders gorgeous. If you look at the comparison images, you can tell it's ultimately the same image, but with a tiny bit of cleanup work done.
Finally, there's a chance that the shader simply broke at some point with these last few updates (I haven't been actively following the updates, but I will check soon). If you look in your log.txt file and see either ALERT or ERROR at the start of any line, then it is guaranteed that the shader didn't take. If you don't see it, it's still possible it didn't take, but it wasn't detected.
If something happened, I'll update the mod to fix it. (Maybe some further improvements will also be put in while I'm at it.)
