Non intrusive current sensor with unreliable (strange) readings
Every time you use a real clamp meter, you should zero it out before measuring.

The hall effect sensors you describe are the same way. There's magnetic pull from the earth and other sources that need to be corrected for. When you draw 5 or 10 amps, that noise is masked out. They are likely still apart roughly the same # of ma as the baseline reading. 

Once you subtract the no-load load from each, maybe on startup, you should get a lot better readings in terms of accuracy and precision.