Okay, I tried a few things out and removed everything which possibly could remove these links or something like that.
In between it even worked, but I didn't change anything consciously (seems I am wrong) and now it doesn't work anymore... -.-
The output link list of print(tag) does show many links, but there is not one with the id 'jtoc_next' which I tried to use. How can it be that this tag is just not in there??
Does remove_tags prevent the links/tags from showing up? Shouldn't it be in there at least when I don't use it entirely?