Zen ID changing on every item page

Version 1.5.1 installed

After having restored a database backup (database backup was working with 1.5.1) I encountered a number of issues:

1. When going to admin page it displayed message requiring databse upgrade from 1.3.9 to 1.5.0
2. Items could not be added to card and users could not login. Both situations caused Whoops Timeout error.

I fixed part 1 by upgrading database only using ZC_install and am now current to 1.5.1 but I am still encountering session issues.

I have not made any changes in configs, PHP or other files. HTTPS seems to be fine.
URL for website is ```html
http://www.mariposaonline.it

Here is Admin-Sessions settings
Cookie Domain True
Force Cookie Use	False
Check SSL Session ID False
Check User Agent	 False
Check IP Address	False
Prevent Spider Sessions True
Recreate Session	False
IP to Host Conversion Status true 
Use root path for cookie path	False
Add period prefix to cookie domain	True

I have also checked Sessions SQL table and the sessions are created there. 

Any advice is greatly appreciated!

Thank you!