Just a quick follow-up and thank you to all that tried to help . . .

Not today, but soon I will upgrade my local Postgres from v14.4 to the latest v17.2. Maybe that will correct it.

Today, I did upgrade ExpressJS on my server from 4.18.1 to 4.21.2.

In the client code, I'm performing this on-the-fly conversion:

const newSession: SessionType = {
  ...sessionContainer.state,
    user: {
      ...userData,
      maxBytes: Number(userData.maxBytes),
      byteCount: Number(userData.byteCount)
    }
  };

  sessionContainer.setState(newSession);
};

And indeed, the two values in question are correctly being converted from strings to numbers.

Once again, thank you all for your great help!