@mo @nano in sure I saw different results depending on which I plugged in first.
Also changing the data mode affected charging.

And I'm sure I had a device on a wall charger change between fast and show charge depending on which side up it's connected to.

Plus my new Surface laptop CAN charge over wall USB-C to C. But battery brick C to C... Well I have seen it work multiple times. But it's not reproducible. Sometimes it works after an amount of plugging and unplugging various ends and directions, but I can't determine a reliable incantation.