Figure out meaning of "Unknown2"

[RevZero]

Refers to the value that can be viewed on the Diagnostic tab in the column "Unknown2".

Bytes 8-11 in savegame file.

Could be a checksum.

[danarcher]

@RevZero I believe that's the header checksum, which much investigation revealed to be a BZip2 CRC32 algorithm: sample code to compute at https://github.com/danarcher/XCom2ModTool/blob/master/SaveGameFormat.md. My rather WIP tool can compute matching checksums with this algorithm.