You may face an issue where you're unable to access all school sites within the Admin Center, although you are logged in, a "Login Required" error appears.
If you use your credentials again, it doesn't work and returns "Oops! The login name and password do not match":
This issue happens because of a delay in regenerating the needed authentication token for your account to access the site. This is expected in such scenarios since you are logging in to different school sites using a single account. If you click on the site again the error should not show up anymore.
Regarding any concerns about your work being delayed/lost, you should not be concerned as this error shows when trying to log in and not when already logged in. While working on the website, you will not be logged off due to this issue and your data will not be lost suddenly.