Currently the server is not under maintenance, so it is likely a launcher issue. We do have a few suggestions for this!
To fix this issue, we recommend trying to run the launcher as an administrator (Head to the installation folder at C:\Program Files (x86)\Zenimax Online\Launcher, right click the Bethesda.net launcher, then select Run as administrator).
If that doesn't fix the problem, you will have to delete the launcher folder (default path C:\Program Files (x86)\Zenimax Online\Launcher), and then download the launcher from the account management page https://account.elderscrollsonline.com to reinstall the launcher.