If your website’s PHP version Because PHP is not the same as the PHP version in your backup, it may cause issues with the proper operation of your website and with some applications. This is more common when migrating from PHP 5 to PHP 7.
We recommend that users regularly backup their WordPress sites or network of sites. You can also use the All-in-One WP Migration plugin extensions to set up automatic backups. Make sure your plugin version is always up to date.
In most cases, the PHP update will have no effect on WordPress or popular plugins or themes. However, it is possible that some plugins, themes, or other functionalities will cease to function.
Set the WP_DEBUG constant to true in your wp-config.php file to see all errors, warnings, and notes generated by the website during execution. This will assist you in locating any problems.
If your install is stuck at “restoring X% files,” “restoring database,” or “activating mu-plugins”
1. Leave the plugin running for another 15 minutes while it is on “Restoring database.”
2. After 15 minutes, open another tab and attempt to login to wp-admin using the exported site’s WP Admin username and password.
3. Save the permalinks structure twice by going to settings -> permalinks.
Your website should now be successfully migrated.
If it isn’t and you receive a 500 error, please edit your wp-config.php file and set WP_DEBUG to true, then refresh the page to see an error. This may assist you in determining the problem, or you can share the error with the Servmask support team for assistance.
Could it be my server settings?
Memory limit needs to be at 256M, max_execution_time to 500, and mysql.connect_timeout to 400. You can find these settings by uploading this file. (https://www.dropbox.com/s/ize8t2k4nww5iq7/phpinfo.php?dl=0) in wp-content of your imported site and then open http://YOURDOMAINNAME.COM/wp-content/phpinfo.php. (tip – use Ctr F search the data that you get)
Source :
https://help.servmask.com/knowledgebase/migrate-wordpress-from-php-5-to-php-7/