Update: For those who might hit this, it looks like the issue was that I wasn't running the latest server version (32.12). This was a surprise since the batch file that launches the server checks for an update first. However, it looks like it doesn't pause and let that update finish - it launches the check, then launches the server immediately after. And I'm guessing the server running causes the update process that's already happening in background to fail. Simply updating server manually, then running the server fixed everything.