Mac OS X 10.11.4 Breaks Some Cisco IPsec VPN Connections

The latest OS X update, 10.11.4, broke some VPN profiles, specifically certain Cisco IPsec profiles. When I first discovered the VPN client wouldn’t connect to a Cisco IPsec profile that was working just fine before the update, I first thought it may be a problem on the remote end, or even perhaps with my ISP. I tried a secondary VPN profile that’s L2TP over IPsec and had no issues.