When an event is archived the subdomain (website URL) is made available to new events. If you have re-used the same URL for a new event this can affect the archived site's navigation.
To access pages from an archived event with broken links add the slug of the page you want to access to the domain of the event website.
As an example, let's say the event website URL is:
For the schedule page, which has the slug "/schedule" you would simply add: