Site under maintenance
Short maintenance string (maintenance.siteUnderMaintenance) used as a title/label when the site is in maintenance.
Why this happens
Full-site (or equivalent) maintenance is active. Longer visitor body: This site is temporarily under maintenance. Please check back soon.
Diagnose and fix
1. Visitors: wait; check back later.
2. Admin: see the admin banner article; disable maintenance when done.
3. See Full site maintenance / Maintenance page content.
4. Partial outages: download/upload maintenance messages instead.