HX711 sporadic wrong values
I get fairly accurate values most of the time however, at times I suddenly get a junk value. 


if you use the ebay board, it has the incorrect grounding, which may contribute to the sporadic values you saw.


  For example, I call the weight function every 3 seconds


poor quality libraries could be another possibility.

I have used the board quite extensively and aside from its tempco, it is fairly reliable. you can see here: https://dannyelectronics.wordpress.com/2015/10/25/a-hx711-based-milliohm-meter/

when everything is done right (and in a constant temperature environment), it has very good consistency.