I would like to know where did you see the checksum is 0 in IPv4 header?
And, could you please let me know which impact you get when you found the checksum value is 0. Based on my knowledge, there is one known-issue may be related to yours. Please try disabling the ikev2 on the rras server.
1. Create the registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\RasMan\IKEv2
2. Create a REG_DWORD value “Disabled” and set it to 1.
3. Restart the services rasman and remoteaccess
Microsoft is conducting an online survey to understand your opinion of the Technet Web site. If you choose to participate, the online survey will be presented to you when you leave the Technet Web site.