JOSM doesn't provide indication during upload that the server is sending 410 Gone errors
When uploading data that deletes nodes which have already been deleted on the server JOSM will just show:
Uploding data... Updating changeset...
It should instead give a more direct indication that some of the objects it's trying to delete have already been deleted on the server. Some changesets can have lots of these and before I investigated further I thought JOSM was stuck in an infinite upload loop.