@SNLLC and @Anonymous, I haven't noticed anything on my end. Are you still having issues?

Instead of clearing cache, there's another way you can test to see if the problem is on the server end. Open a private/incognito window in your browser - this doesn't use the same caching data, so it's "refreshed" in a sense. If you can log into QBO without any problems, it's not your cache. It may not necessarily be a server problem on our end, but you (probably) don't need to clear anything in your regular browser window. 

A simple fix that goes a long way in fixing lots of web-based programs (QBO included).