hello Einstein,
i used the motion effect, not motion blur.
also tried mixing scale and position to get the same effect but results are the same.
i tried creating a new project with only the image to pan and the export is perfect, it pans smoothly as it is supposed to do, so i tried adding a text with fade in and fade out and a position fx (as in the original project) and still the exported video is perfect.
so i'm starting to think it's a pc performance related problem?
maybe it struggles rendering both the high res image pan and the text above it?