If the title of a webpage that belongs to you or is visiting is saying Maintenance, it is usually an indication that the plugins (usually WordPress) are being updated especially if the following message appears in the body of the page.
Briefly unavailable for scheduled maintenance. Check back in a minute.
Wait 60 seconds and then refresh the page and the content should load. Hopefully, you were nor fulling out a form at the time as the info may get wiped out in the process.