Could you help us understand the issue more?
What happens when you invoke the update manually, using the VSE Console?
Do you know what Update tasks are scheduled (whether they are local or via ePO), and when they are scheduled to occur?
Because, it sounds like you have an Update task scheduled to run on Startup.
And instead you might want to choose a Daily update - just look at how the task is configured, and set it to what you want it to be. But if you are ePO managed, you should talk to your ePO administrator instead.