It seems as though the support for using DHCP interfaces with IPsec VTIs was dropped from 1.2.1 to 1.2.1-s2. Below is the commit error I am receiving:
vyos@pr140002-WalshHQ-1# commit [ vpn ] VPN VTI configuration error: Invalid local-address "", an ip address must be specified for VTIs. [[vpn]] failed Commit failed 
The /config/config.boot file that was tested without error in 1.2.1 is now producing errors that we received during 1.2.x EPA testing. The config file used for testing is attached to this ticket.