I was able to get this working very quickly, but the values coming from the HX711, with no load on the bar, kept drifting very significantly.

After a long troubleshooting session, I found out that the HX711 print has a major design flaw. They forgot to connect the AGND pin of the HX711 to GND, so it's just floating in the air, explaining the drifting. This can be fixed by soldering a wire between the GND pin on one connector and the E- pin on the other side. I found the exact same board on a different site with a picture of the schematics. This confirms that AGND is not connected to GND. See attached picture.

It's also important to note that the print is designed to be supplied with 5V, even though the HX711 is specified to work down to 2.6V. The internal voltage regulator on the HX711 is configured with R12 and R13 to produce 4.2V across the sensor (E+ and E-). Considering the drop across the transistor, the supply voltage needs to be about 4.5V (or up to 5.5V), otherwise the regulator can't do its job. If a 3.3V supply is provided, the resistors can be changed accordingly. If you use it as is on 3.3V, be aware that the built-in regulator will not be able to do its job, so any ripple on the supply voltage will influence the measurement.

Tested on a Professional instrument, and accuracy is within +- 5%, acceptable for this price.