If nothing is found, then might be worth creating an exception. And to be on safe side, would be great to check with Norton support for confirmation - if your license allows free support cases. 

it means Norton 360 detected that the laptop was attempting multiple failed connections to an SMB share on the network, which is a sign of a possible brute force attack. as a protective measure, Norton’s IPS flagged this as suspicious and blocked the laptop’s IPv6 address to prevent further access.

accordingly, you need to ensure that the laptop is using the correct username and password when accessing the network resources. if there was a misconfiguration or a change in credentials, it might have caused the repeated failed login attempts.

if the laptop can be trusted after running full scan against viruses and malwares, you can manually remove the block from Norton’s Remote Access Protection settings and allow it to reconnect to the mapped drive.

Any additional thoughts on what may have happened?

as indicated above, it could be caused by several failed login attempts due to incorrect username and password.