When using a QQ1 TableView backed by a simple QAbstractTableModel, if the role names (and thus corresponding columns' role names) are set to numeric values, e.g. "0", "1", QAbstractTableModel::data(...) is never called, and the cells in the TableView are empty. If on the other hand role names such as "column 0", "column 1" are used, everything works as expected.
It's not clear to me at the moment whether this problem is on the model side, or the view side, but knowing what QQ1 TableView is like, I would suspect it's the latter.
This bug is new to 5.12; it does not occur on 5.11. Please see attached test case.