As mentioned previously, the 20A shunt should be 0.01 ohms, yielding a 200.0mV drop at 20A. If the 200mV range is accurate, I can only think of two ways the meter could read 10X the expected reading: 1) the shunt resistance has gone up, or 2) the wrong decimal point is on.
The current path for the 20A range is very short, straight from the 20A jack, across the shunt and back to the COM jack. So if the voltage drop has gone up, there aren't too many causes other than the shunt, the copper, and the solder joints. The rest of the circuit should be a fairly straight path to the 200mV F.S. input of the 7106.
The best way to measure the shunt is to pass a known current through it and measure the voltage drop between the black wire (marked "20A" on the PCB) and the COM jack. You'll need at least 500mA to get a good 5.0mV reading.
In 20A range, the display should be configured to display "19.99" max. The 7106 does not have decimal point drivers, that would be handled externally by the range switch. It is likely that the 4070 CMOS IC beside the 7106 is the DP driver.
Edit: I see lowimpedance had the same DP idea...