4.1.2 Check that the SIG , G1 and G2 wires are properly and tightly connected from meter to shunt. This is usually caused by a miswired shunt in the system. Make sure the missing current flows through the shunt to get to the battery. For example, if solar panels or solar charge controller are connected directly to the negative terminal of the battery instead of the other side of the shunt then the current from the panels goes directly into the battery without going through the shunt, so the meter will not measure the charge current from this source. Rewire if necessary.
Amps always show charging when discharging, and vice versa.
Probably the connections to the Kelvin terminals on the shunt are reversed, so that SIG terminals need to be reversed with the G1, G2 wires at the shunt. Check wiring diagram 4.4. If not, meter is probably defective. For example, a radio, stereo or TV will use changing current depending on the sound level, or picture brightness. If some clouds are present, charging current from solar panels may vary somewhat depending on cloud position, even when brightness does not appear to change significantly.