I don't understand why I frequently - daily - get a 'green gear' in the upper right - please explain...
We often deploy minor changes on a daily basis. When you see the gear icon is green, that means that a significant change has been made in the web core that needs to be applied. This notifies you that a there's an update and allows you to apply the change on a time of your convenience thus preventing a refresh of Todoist occurring on a bad time.
Often, you will not see a visual difference as most changes are related to the backend. However, expect to see the green icon every now and then as we are constantly improving Todoist. :-)