Hi Sean, thanks for your reply. Just to be 100% clear for the developers, I was doing the following:
file -> new batch job
set and upscaling on a single dimension (x dimension)
clicked on the elipse and changed the resampler, everything else remains default
Changed the output folder to a sub folder of my input folder
Imported all image in my input folder (about 30)
With that methods, regardless of the sampler I chose it uses the same one. I think it was nearest neighbour, even though the default is bilinear.
I am running AFPhoto V18.104.22.168