If you're using the Classic Translation Editor, you could have trouble finishing a larger page's translation. For example, a page that has been 100% translated and saved may appear to be only 80% translated.
You can fix this by increasing the max_input_vars setting in your PHP configuration.
Add or edit the following lines into your php.ini or .htaccess files, depending on your hosting provider:
max_input_vars = 10000
php_value max_input_vars 10000