Interactions there were on an account are no longer on the account. They were not sts 'D'. Other accounts can be found that have an interaction that did not previously have them.
This can happen if the user changes the Account id on the Interaction on Customer Service Entry. Users tend to do this believing that it brings them to the interactions for another account, but it actually changes the account id for the interaction that they were on.
Here is the correct way to navigate to another account: users need to click the binoculars at the top (or click F3) to bring up the Find Interactions window and search for the new account.