Slowed to a Crawl
Suddenly my Duolingo interface has slowed down, and when I complete a level and try to continue, it gives me the spinning circle and never goes on to log that level and show me the progress graphics. I finally have to just quit. My internet is no slower than usual (download 35, upload 6.6).
That usually means problems with internet access. Download and upload speed aren't the numbers you care about - it's the latency and reliability that matter. It's also possible for problems to come from other sources - in my case, my rubbish Technicolor router runs out of memory to manage new connections. Try rebooting your router and see what happens.