I moved my Wordpress website using Duplicator and now strange things are happening!

Hello,

I hope you can help me with a problem that is now driving me nuts!

I moved my completely functioning WP site from my dev server (Dreamhost VPS) to its live server (I think Hostgator run) using the Duplicator plugin.

After resolving some permissions issues, everything on the front end (and most of the backend) seems to be working fine, except for a few odd things, which I am only bundling together because I think they may be related.

Some of the 'odd things' include:

- Defender tries to run a scan and I just get a popup stating 'undefined'. Also, I can not enable audit logging.

- I try to license my theme (X Theme) and while it initially confirms validation, it instantly goes back to being 'not validated'.

- After adding a new user, I just get a blank useless user entry which I can't delete.

-Trying to auto update WP, I get a message 'update already in progress' which never goes away.

I have tried everything I can think of (and search for) including:

- Reinstalling / deactivating themes & plugins
- Manually updating all WP files
- Changing PHP versions
- Optimising databases
- Checking all file/folder permissions

After enabling debug, I get the following errors when trying to add a user:

WordPress database error: [Duplicate entry '0' for key 'PRIMARY']
INSERT INTO <code>wp_sputsq_users</code> (<code>user_pass</code>, <code>user_email</code>, <code>user_url</code>, <code>user_nicename</code>, <code>display_name</code>, <code>user_registered</code>, <code>user_login</code>) VALUES ('$P$BDGASMucIHaHVAR9pliYT4iia/yBxl0', 'hello@theme.co', '', 'themeco', 'themeco', '2016-09-19 12:44:09', 'themeco')

Notice: Trying to get property of non-object in /home/ownersli/public_html/wp-includes/pluggable.php on line 1723

Notice: Trying to get property of non-object in /home/ownersli/public_html/wp-includes/pluggable.php on line 1724

Warning: Cannot modify header information - headers already sent by (output started at /home/ownersli/public_html/wp-includes/wp-db.php:1396) in /home/ownersli/public_html/wp-includes/pluggable.php on line 1174

Everything I can find about this talks about blank spaces in PHP code and as far as I can tell, I have checked for this (and reinstalled the files mentioned).

Any words of wisdom?

BTW, I am not a developer and very new to all this, so I may be missing something really obvious!!