It looks like the import has now finished. I’ve reset the Tumblr importer so if your site is missing content, please try running the import again and be sure to leave your Tumblr account connected — otherwise this can prevent the import from starting.
We’re processing quite a few imports from Tumblr at the moment, which is causing a backlog of imports in our system. While it may look like your import failed, it’s just in line for processing, and luckily it’s still in the queue. At this point I’m not able to give an estimate on how long it might take to catch up with the backlog, though.