Got the same issue here. I've found that the inability to import lies within the metadata of the webloc file itself. In my case, exporting the bookmarks to file management in Finder, then compressing them with 7ZIP, not ZIP, will upon import, target the disk location of the webloc file itself, and resulting in a blank browser display at launch, effectively erasing webloc files of their original internet location target, perhaps the resource fork data. It is now a file consisting of the title only. Hope this sheds some light on the deal.