Why can my consolidation journal entry balance but still be wrong?

A consolidation entry can balance mechanically while still using the wrong accounts or the wrong reporting layer.

For an acquisition-date elimination, you need to remove the parent's investment and the subsidiary's acquisition-date equity, recognize fair value adjustments, recognize any goodwill, and include noncontrolling interest if the parent owns less than 100%. If you force the debits and credits to balance but omit the fair value adjustment or noncontrolling interest, the entry may look tidy while producing the wrong consolidated statements.

Balance is necessary, but it is not enough. The entry also has to eliminate the right relationship.