Cannot open any lessons, just returns to home page.
I can go into all the unlocked topics, but when I try to open any specific lesson or strengthen the skill, it instead takes me back to the home page (the overall tree). I've tried refreshing, restarting my browser and computer, using Safari instead of Chrome, clearing browser cookies, and typing in the url of the lesson manually. Nothing has worked so far.
Another weird thing is that this is only happening for my Norwegian and Dutch lessons; my French ones are working perfectly.
Any suggestions/ similar experiences?
Sounds like a bug. I would report it in Troubleshooting, since this is where Duo staff typically looks, and then maybe try signing out and in again (though it sounds like you already did.) Best of luck! :)
Not yet, I have it posted in the troubleshooting discussion too, here: https://www.duolingo.com/comment/22903813$comment_id=22903860 so you can track that one too if you want!