As I read it they extracted more gold than they thought from...

As I read it they extracted more gold than they thought from their reserves, the problem was that the head grade was lower and thus lower revenue/period. PoG also went down during the half year and low grade stock piles correctly written off.

On page 2 of their announcement of 22/2 a footnote says:
:
"The Company acknowledges that mining operations conducted to date have not achieved all of the Modifying Factors used to estimate the Ore Reserve. However, the operational issues continue to be reviewed, and Missouri is considered to be an early stage operation and the Company has not formed any conclusions that would materially impact Modifying Factors. A work stream has commenced that involves in-depth analysisof the operation and all the available technical data with the view to implementing remedial action to minimise the potential impacts on the Ore Reserve estimate. Any future updates to the Ore Reserve estimate will consider the actual performance of the operation in conjunction with typical industry parameters, to arrive at a position on the appropriate Modifying Factors to apply to the estimate, such that they continue to align with expected and achievable outcomes"