I had something similar happen to me, if you still have FTP access it could be an easy fix. One of my sites was stuck in maintenance mode from a Jetpack auto-update. I went into the root WordPress folder and removed the “.maintenance” file to fix it. Or if that doesn’t work, use FTP to go into the “/wp-content/plugins” folder and rename the Jetpack folder to something like “_jetpack” to disable it temporarily.