Yep. First playlists.net sent me through an endless log-in loop of "Can't find that page," then trying to upload a playlist gets "No active transaction" in both Chrome and Edge. Apparently this happens when the site that has to do the heavy lifting (Playlists) doesn't recognize add-ins or apps on the side where it's getting the data (Spotify).
Playlists.net definitely is granted access to my Spotify account. There are a handful of fan-engagement apps that also have access, plus lastfm and Facebook. At least some of these had access the last time I successfully uploaded a Playlist, and I'm not eager to turn off all of them until someone at Spotify indicates that one is causing the problem, as these are all normal apps that a lot of listeners have.
I had a similar problem, the message I got was: "There was a problem submitting your playlist. Please refresh the page and try again." I tried refreshing several times and nothing, I tried with IE and Firefox browsers and didn't work, then I tried with Chrome and it worked perfect!