[REG] Add and remove rows much slower in 5.12.x versus 5.11.x

QList<QList<QStandardItem *>> QStandardItemList
QStandardItemModel *metaDataModel = new QStandardItemModel;

//remove Rows (could be hundreds or even thousands - the more rows the longer it takes)
>if(rowNumber > NUMBER_ROWS_TO_DISPLAY)
 {
    int  numberOfRowsToRemove = rowNumber - NUMBER_ROWS_TO_DISPLAY;
     //this next command is very slow on 5.12 but very fast in 5.11
     rowNumber -=    numberOfRowsToRemove;
    metaDataModel->removeRows(0,   numberOfRowsToRemove, QModelIndex());
}
//Add a row  (could be hundreds or thousands of rows)
for(rowIterator = 0; rowIterator < QStandardItemList.size(); rowIterator++)
{ 
     //Insert Rows
     //This is also slower in 5.12 but very fast in 5.11
     metaDataModel->setItem(rowNumber, 0, QStandardItemList[rowIterator][colNum]);
     for (columnIterator = 1; columnIterator < QStandardItemList[rowIterator].size(); columnIterator++)
    {
        metaDataModel->setItem(rowNumber, columnIterator, QStandardItemList[rowIterator]   [columnIterator]);
    }
    metaDataModel->setItem(rowNumber, 0, QStandardItemList[rowIterator][colNum]);
    rowNumber++
}