xcube gen: indexes along dimension 'y' are not equal

[forman]

When using xcube gen with processed variables that use flag values, we now get errors such as

step 2 of 9: computing variables...
Internal error: failed computing valid mask for 'rrs_560' from expression  'np.logical_not(PIXEL_CLASSIFY_FLAGS.F_INVALID)': indexes along dimension 'y' are not equal

The error happens in code that used to run without problems. Must be due to a change in xarray or deeper.

Here is the full traceback:

step 1 of 9: pre-processing dataset...
  pre-processing dataset completed in 1.6446000000058802e-05 seconds
step 2 of 9: computing variables...
Internal error: failed computing valid mask for 'rrs_560' from expression 'np.logical_not(PIXEL_CLASSIFY_FLAGS.F_INVALID)': indexes along dimension 'y' are not equal
Traceback (most recent call last):
  File "d:\projects\xcube\xcube\util\expression.py", line 49, in compute_expr
    result = eval(expr, namespace, None)
  File "<string>", line 1, in <module>
  File "d:\projects\xcube\xcube\util\maskset.py", line 98, in __getattr__
    return self.get_mask(name)
  File "d:\projects\xcube\xcube\util\maskset.py", line 128, in get_mask
    mask_var = mask_var.where((flag_var & flag_mask) != 0, 0)
  File "D:\Miniconda3\envs\xcube\lib\site-packages\xarray\core\common.py", line 859, in where
    return ops.where_method(self, cond, other)
  File "D:\Miniconda3\envs\xcube\lib\site-packages\xarray\core\ops.py", line 191, in where_method
    keep_attrs=True)
  File "D:\Miniconda3\envs\xcube\lib\site-packages\xarray\core\computation.py", line 969, in apply_ufunc
    keep_attrs=keep_attrs)
  File "D:\Miniconda3\envs\xcube\lib\site-packages\xarray\core\computation.py", line 209, in apply_dataarray_vfunc
    raise_on_invalid=False)
  File "D:\Miniconda3\envs\xcube\lib\site-packages\xarray\core\alignment.py", line 217, in deep_align
    exclude=exclude)
  File "D:\Miniconda3\envs\xcube\lib\site-packages\xarray\core\alignment.py", line 132, in align
    .format(dim))
ValueError: indexes along dimension 'y' are not equal

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "D:/Projects/xcube/xcube/cli/cli.py", line 257, in main
    exit_code = cli.main(args=args, obj=ctx_obj, standalone_mode=False)
  File "D:\Miniconda3\envs\xcube\lib\site-packages\click\core.py", line 717, in main
    rv = self.invoke(ctx)
  File "D:\Miniconda3\envs\xcube\lib\site-packages\click\core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "D:\Miniconda3\envs\xcube\lib\site-packages\click\core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "D:\Miniconda3\envs\xcube\lib\site-packages\click\core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "d:\projects\xcube\xcube\cli\gen.py", line 126, in gen
    **config)
  File "d:\projects\xcube\xcube\api\gen\gen.py", line 142, in gen_cube
    monitor)
  File "d:\projects\xcube\xcube\api\gen\gen.py", line 284, in _process_l2_input
    dataset = transform(dataset)
  File "d:\projects\xcube\xcube\api\gen\gen.py", line 207, in step2
    return compute_dataset(dataset, processed_variables=processed_variables)
  File "d:\projects\xcube\xcube\api\compute.py", line 113, in compute_dataset
    errors=errors)
  File "d:\projects\xcube\xcube\util\expression.py", line 32, in compute_array_expr
    return compute_expr(expr, namespace=namespace, errors=errors, result_name=result_name)
  File "d:\projects\xcube\xcube\util\expression.py", line 57, in compute_expr
    raise ValueError(msg) from e
ValueError: failed computing valid mask for 'rrs_560' from expression 'np.logical_not(PIXEL_CLASSIFY_FLAGS.F_INVALID)': indexes along dimension 'y' are not equal

[forman]

Strange enough, this doesn't seem to covered by tests.