The most recent commit on master of NAS2D which is compatible with op2-landlord is:
9e6855a86546a90bde70a97698c0387f93f7f5db
GitHub Pull-Request for Submodule reference:
Add NAS2D submodule #1@leeor_net, you've been invited back to the OutpostUniverse organization.
I noticed you have a version of the repository on your personal account, which appears to be older. The Pull-Request defaulted to the original repository.
Edit: Oh, and side note. With some very minor modifications, the project builds on Linux. The one main problem is the call to
freopen_s. It seems this method is a C11 extension, and many C++17 libraries still only reference C99. Switching out the call to use
freopen (the non-secure version) allows the code to compile on Linux. I suspect that would result in a compiler warning on Windows though, due to the use of the non-secure version.