You could try freezing subdivisions in both subtools before merging. Then uncheck Freeze Subdivision levels once they’re a single subtool.
I just tried it on parts of the demo soldier the bracelets and kneepads. simply creasing, then subdividing and merging produces a mesh wherethe bracelets lose creasing.
Freezing subdivisions before merging works fine.
Worked this time, hopefully it’s a viable solution for you.