Repl.it's workspace operates on quite a few plugins, and any plugin can crash. This isn't too uncommon to happen, I've had it before. Usually a refresh fixes the problem. If not, try signing in and out again, and maybe clear the cache. If that doesn't work, make sure your firewall or proxy (if you have one) isn't blocking any repl.it plugins. If the problem persists, you'll probably have to get in contact with some staff.
Hope this helps. :)