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I am trying to implement this solution (How to merge single polygons to multi part polygons by maximum distances?), but when I create a buffer around my polygons, those with holes are ignored. I tried to Delete Holes using the processing tool. It does fill the "real" holes but these features:
are not filled in. Polygons with these are also ignored when I try to buffer them...
If I try to fix them manually, I get this:
Also, these polygons were created from a raster using polygonize. How do I go about being able to create a buffer around such polygons?