Products not adding to cart 3.0.2.0

Hi,
Running OC 3.0.2.0 on a dedicated Plesk server (new). Been running OK for a few weeks with occassional error messages.
www.rufuspublications.com
We are running the Journal theme.
Today we installed a Pre-order Module and a Quick Order Status module. We then noticed that although we weren't getting an error message, products were not being added to the cart (it says success but isn't).
So we uninstalled the modules. It still doesn't work.
These are the messages from the error log:
2018-10-11 14:42:44 - PHP Notice: Undefined variable: categories_info in /var/www/vhosts/rufuspublications.com/httpdocs/system/storage/modification/catalog/controller/common/header.php on line 102
2018-10-11 14:49:15 - PHP Warning: unlink(/var/www/vhosts/rufuspublications.com/httpdocs/system/storage/cache/cache.catalog.language.1539272951): No such file or directory in /var/www/vhosts/rufuspublications.com/httpdocs/system/library/cache/file.php on line 68
2018-10-11 14:59:03 - PHP Notice: Undefined index: name in /var/www/vhosts/rufuspublications.com/httpdocs/system/storage/modification/catalog/controller/common/header.php on line 102

Any thoughts?

KR

Mark

Well, this all concerns a paid Custom Theme, and probably some paid
Extensions as well, so, the right place here would be the commercial Forum,
since this all is not about OpenSource, but commercially licensed Code.
Ernie

Prior to create a new service request in the Commercial Support section of the forum, since this issue is about an extension, contact the extension developer first in order to see if this issue can be resolved.