In Cisco Secure Firewall Management Center (FMC), when two users attempt to modify a VPN policy simultaneously, the system implements a locking mechanism to prevent conflicts. The first user who selects edit on the policy locks the configuration, preventing other users from making changes until the lock is released.
Steps:
* When the first user selects edit on the VPN policy, FMC locks the policy for editing.
* The lock ensures that only the first user can make changes.
* Once the first user saves or cancels their changes, the lock is released.
* Other users can then edit the policy.
This locking mechanism ensures that configuration conflicts are avoided and only one set of changes is applied at a time.
References: Cisco Secure Firewall Management Center Configuration Guide, Chapter on Policy Management and User Permissions.

Reference: https://www.cisco.com/c/en/us/td/docs/security/firepower/620/relnotes
/Firepower_System_Release_Notes_Version_620/new_features_and_functionality.html