If you ever “imported contacts”, perhaps from your GMail address book, then LinkedIn will offer you those repeatedly as new connections to “invite” to your network.

If you want to stop that, go to https://www.linkedin.com/mynetwork/contacts/imported/ then select all and Delete them. Note that this will not delete anyone from your LinkedIn connections, just the pointless email contacts.

If everything went well, the above URL should now display something like “You don’t have any imported contacts”. Congratulations!