Solar inverter stops drawing power from PV
Usually MPPT charge controller have ability to select Main Source for their input. Make sure PV is the main option here and Grid Utility for backup. if you make sure this point is correct, then
Input for MPPT must meet the minimum requirements. for example if you choose utility as the main source, say it's in 220V system, the MPPT will keep it as main source as long as the voltage not drop to lower than 170 or any number depend on your MPPT manual. So, in your case, maybe your PV has not meet the minimum voltage that MPPT want, maybe because of cable joint malfunction or something else. measure your input from PV to MPPT. 
Battery can also be a problem here, if the battery fail to suply power, because the voltage too low or another problem, MPPT will choose the safest way to feed their output. Measure your battery and make sure the voltage higher than 10.5 volt.
Read MPPT manual :-)