Printing a g_warning() from the library is not helpful.
Client-side, libnm should support newer server versions and changing
formats. To support forward-compatibility, it should parse the received
GVariant best-effort like, without complaining.
Server-side, libnm-core should return errors when receiving invalid
configuration. It must not maintain forward-compatibility, only
backward-compatibility -- which is implemented by handling old
and newer formats. But never should server allow a configuration
that is invalid.
Currently, the libnm API cannot yet fail at this point. Hence,
it cannot return an error. It would need a strict and relaxed
parsing mode. Until that exists, just comment out the warnings.