Solar inverter reports full output but the meter shows half

What we told them

The inverter is measuring generation and the meter is measuring export — those are different numbers by definition, and the gap is your own consumption. Before assuming a fault, check what the house was drawing during daylight: immersion heaters and heat pumps routinely account for exactly this discrepancy. Compare inverter output against a whole-house consumption monitor rather than against the export meter. If they still disagree after that, then the inverter is worth testing.