We've had some unconfirmed reports of difficulty accessing the draw.io site from the Crimea. We have no blocks on any IP range, but we are hosting using Google App Engine. We have seen Google IP address ranges being blocked from certain locations (outbound blocking, not Google inbound) so that the draw.io site is not accessible.
If you ever have problems accessing the main site, there is a backup site at https://jgraph.github.io/draw.io/war/index.html. This is the gh-pages published branch of the repository in Github. It is kept up to date, but note that it isn't tested the same way the main site is. You can still report bugs on it, as for the main site.
It's also not intended to be used with Google Drive or Dropbox. If you have Drive or Dropbox sync'ed to your local filesystem, we suggest you work with the files locally (you can drag and drop them into the draw client).