Thanks for your attention and suggestions. I left it a while then tried in a different browser, where things worked fine. While I'm a free user, I only ever use a browser and an iPhone app. Not sure how changing browsers could have got around the device limit if that were the problem - wouldn't that have maybe looked like I was trying to use an extra device?
Thanks also for the status link - I'll be sure to check that in case of problems in the future, though none were noted today. Glad it was working for you smoothly!