I don't know if this was the same problem that HolyChrome was having, but I've been experiencing intermittent disconnections on the web client, too. I'll be playing as normal, then the little stat window in the upper-left hand corner will go red, and the login scroll will pop up after a few seconds. I can manually log back in. The client window/tab doesn't close or even register a disconnection (with the "save as HTML log," "reconnect," and "quit" buttons).
Sometimes, usually in the wee hours of the morning after several other DCs, the login scroll never comes up. Refreshing the tab with the web client gives a generic 404 error page, which persists until I restart the browser and clear all the sindome.org data from the cache.
This was happening before a few months ago, but it stopped without explanation. Running the web client on FF 66.0.5 x64. Internet connectivity remains constant throughout.