I have the same, classic web page - specifically when I move the progress sort order to release date, page craps out to 500.
Fix just went up. Apologies on the error. This one was from moving our released date tracking to a new data source and I missed a condition on the progress page.
Trakt Web: Home .. v2. Stil not working for me, I still see nothing in Up Next and just a swirling circle. Logged out, clearn cache, cookies, everything and logged back in again. If I click on the progress arrow, I get the info then, but on the main front page, usual go-to Dashboard page, I see nothing 
Did “everything” include Reset Progress Data under Settings-Advanced?
Yeah, I hit Reset Browser Data and Reset Progress Data (got a green bar saying “Your progress cache will be updated in a few minutes.” .. but still the same swirling circle.
Thank you! I am back in action!
After not having much luck with the Reset Progress Data button last night and it still swirling, I hit it off again, and just went to bed. It must have taken longer than a few minutes overnight, but today, I have the Up Next showing again as normal. So happy to say it’s working again for me now.