If you analyze several load cases or combinations in one result combination and define the load cases as "Variable," then zero is shown for the maximum or minimum value at locations with the same signs. When using the "Variable" ("eventual") superposition, it can also happen that no load case or no combination becomes effective. Zero is smaller than the smallest maximum value or greater than the greatest minimum value.
A solution would be to define the load cases or combinations contained in the result combination as "Permanent," for example:
RC1 = CO1/Permanent or CO2/Permanent or CO3/Permanent or CO4/Permanent
The load cases or combination are then compared as permanently acting. Thus, the obtained extreme values are unequal zero also for regions with the same signs.