“a few hours of troubleshooting”? This sucker (me) spent a week in despair and frustration! Even bought a second Pro board to rule out broken hardware. I guess the idea with the resistors is to ensure priority for the USB serial connection (with an FTDI) over the D0/D1 UART. As you say, it is not on th Pro Mini, but some other boards have it the other way around, ie resistors “blocking” the USB serial if there is a conflict in use.
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