Users losing access

Hi All,

I created a new List to replace a list (Customer Requests Database) whose structure wasn't working and named it something similar to the old list (Customer Requests Database 08042024).

After creating the new List I changed the name of the old List to "Old Customer Requests Database" and changed the name of the new list to Customer Requests Database. I then removed security groups from the old list so as to make it hidden from my users and attempted to add those groups to the new list but could no longer find the security groups.

I tried every possible method to find the security groups in other lists/libraries but with no success now the users who could originally access the site now get access denied when attempting to visit the site.

I tried to create a new security group and placed the users in this but still access denied.

Does anyone know why this is happening?

Thanks

Kamil