Hello,
If it works after logging off, then it was probably a temporary problem with hosting or a problem with caching in your browser.
If you can't save even after logging off, then check the browser console to see if there are any errors. Also, you can enable Debug mode in Global Configuration to see if Joomla logs any errors during saving.
Also, you should check if directory permissions are correct and if the folders and files are writable by the server.
Regards,
Milos
