The same thing happened to me. I have WP 5.2 and the plugin updated and the page was no longer accessible.
error message
E_COMPILE_ERROR. require_once() [function.require.php]: Failed opening required ‘/home/xxx/wordpress/wp-content/plugins/backupwordpress/whitelist-html/whitelist-html.php’ (include_path=’.:/usr/local/share/pear’)
Solution for the moment
Go with FTP to your plugin folder and rename the folder old*.*. Now you should be able to log in again in dashboard. Disable the plugin until the plugin is tested with your version.
