Used to work well a couple of days ago. To help you figure out the problem, here is my attempt to type "curl" in cmd prompt:
curl https://dl.dropboxusercontent.com
curl: (6) Could not resolve host: dl.dropboxusercontent.com
In case of error message in Chromium browser, it returns DNS_PROBE_FINISHED_NXDOMAIN error. I have contacted network provider regarding this issue but they recommeneded me to contact Dropbox site instead.
In addition, my network uses following DNS servers: "210.94.11.xxx" and/or "210.94.72.xxx" (digits on "xxx" parts are set randomly whenever checking my DNS server).
Note that switching DNS to CloudFlare or using VPN works.