I have experienced the same issue with Chrome on Apple Mac. SmartThings support could not identify the random “access denied” issue and thought that it was perhaps time of day? It was not!
After a few attempts and rebooting my PC, I think it has to do with an expired or cached browser cookie for SmartThings website. The work around I found to get around this issue is to:
Either clear all your browser based cached cookies (Ugh) or
Simply launch a “New Incognito Window” (or whatever is your browser’s private window), login and edit the devices.
Chrome’s New Incognito window does not use any existing “cached” cookies and after login, you can edit devices.
On top of what Kurt said in the previous post, make sure that you initially log into https://account.smartthings.com. After you login, you are redirected to your correct shard (which may or may not be na04-east2).