Needless to say, that I'm not able to reproduce the issue. If getent {group,passwd} systemd-{network,resolve} work and with the given information, I'm running out of ideas what's specific about your systems which could be causing this.
Maybe you start with a minimal debian system and turn that bit by bit into a system like the one where you encounter the problem to see which change is causing it. You might also try stracing the process. Maybe that gives some clues.
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