wp-login loop

I’m having a problem with logging into the backend of a WP installation.

I moved the installation to a new server – everything else stayed the same. The server is a VPS running Plesk and I’ve hooked up the Plesk services for WP.

When I try to login into wp-login or wp-admin, it just enters a continuous redirect loop. Enter username and password again and again, just get the same login screen.

Things I have done:

i) Checked the access in .htaccess
ii) Checked the URL inside wp-options MySQL table
iii) Switched to another theme to check if that is issue
iv) Cleared the cache in the WP installation
v) Used another browser and then another PC to check browser cookie / cache issues
vi) Run in debug mode – I get this report:

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Notice: wp_register_style was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or login_enqueue_scripts hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3.) in /var/www/vhosts/peter-ould.net/httpdocs/wp-includes/functions.php on line 3787

Notice: wp_register_style was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or login_enqueue_scripts hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3.) in /var/www/vhosts/peter-ould.net/httpdocs/wp-includes/functions.php on line 3787

Notice: The called constructor method for WP_Widget is deprecated since version 4.3.0! Use

__construct()

instead. in /var/www/vhosts/peter-ould.net/httpdocs/wp-includes/functions.php on line 3619

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Still haven’t found a solution – any help gratefully received.