Hi Ben,
first let me thank you very much for your useful tool that fills a huge gap between accessing the Last.fm scrobbling data and doing something useful with it like creating a Spotify playlist with Ivy, another great free online tool. I could successfully get my 188k of scrobbles from my user profile (hjbardenhagen), although two errors were shown in red during the process, but not verbosely what they were. So the end result was not exactly the same number as shown on my profile, perhaps about 400 less. It took about one hour and went fine otherwise.
Long story short: in order to create Spotify playlists with Ivy and your csv files, they should not have more than 10k of scrobbles, because Spotify has a track limit for single playlists at 10k. If the Ivy search result is bigger than that, you cannot copy & paste it to a new playlist in the Spotify desktop software. So it would be useful if you can stop Last.fm to csv at 10k or some point below that, let it write the first csv file and then continue automatically.
Another nice feature would be if we could choose the necessary data in the csv file, as Ivy does not need the album info or scrobbling date and time. It only blows up the size of the csv file which gets too large for Ivy anyhow, e.g. my original 188k scrobbles file (size 17 MB) was not accepted by Ivy, so I had to delete the related columns first and also all multiple scrobbles of the same track which are usually included, but not necessary for a search of the Spotify database. I could eliminate them with a standard filter function in LibreOffice Calc. Afterwards the csv file contained only 62k of unique scrobbles, and the file size came down to 4 MB which could be read by Ivy. It found about two thirds of my Last.fm scrobbles on Spotify (39k) and needed more than seven hours for that, by the way: http://www.ivyishere.org