I double checked with the engineering team and the system is running at optimal best with thousands of users designing simultaneously.
In all probability, what you experienced may be a temporary browser issue due to Cache and Ad Blockers/other extensions.
Adblockers extensions tend to interfere with the design edits and loading of templates.
Hence, clear the cache of your browser, deactivate any ad blocker extension and also you may use incognito mode. You can try to use a separate browser also. (You may use a fresh installation of Opera)