I found and fixed the issue!
The “GBuffer” PP material which reads the scene texture can only output an Emissive Texture!
My solution was to compress the normal map into the 0-1 range
And then Uncompress it again for use in the material
A little bit of rewiring the channels later:
and we have a perfect match!
(See if you can tell which set of tiles are the source and which set of tiles are the atlas)
I hope somebody finds this useful!