Hi!
Thanks for your inputs. I've been trying to fix this several times now, but I can't seem to make it work. At some stage I managed (unintentionally) to delete "something" and all the woods disappeared. I did not create this huge behemoth of a multipolygon in the first place so I don't know much about how/why something is connected or not. i simply try to fix what I broke. If you are able to: can you help me?