I cannot access Dropbox from any of my accounts, from any location (different Wi-Fi), or from any device, whether the app or a web browser. Except from a cellular connection.
We were having the same issue, it looks like it just resolved itself. Here is the tracert before and after.
Whats the errors? What happens?
We need a bit more info here.
Have you checked things like firewall and filtering software? LittleSnitch has also been known to do this
Yet the phone works if you connect via cellular?
The issue then is down to your ISP and the connection between the ISP / devices (firewall/routers etc.) because as you have shown the devices themselves are able to connect and work via a different internet system.
I go back to my original comment then about making sure that its allowed on things like LittleSnitch etc and checking traceroutes etc. to see where its being blocked.
Thanks! Resolved here as well.