SIday: failed to contatenate into a single cube

Migrated Jira Issue CDDSO-24
Jira creation date 21/04/2022 15:23
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Converting SIday variables fails with errors like this:```Unable to produce MIP requested variable "sisnthick" for "CMIP6_SIday": failed to concatenate into a single cube. CellMeasures differ: [[CellMeasure(array([[ 1.00000000e+00, 1.00000000e+00, 1.00000000e+00, ..., 1.00000000e+00, 1.00000000e+00, 1.00000000e+00], [ 1.00000000e+00, 1.00000000e+00, 1.00000000e+00, ..., 1.00000000e+00, 1.00000000e+00, 1.00000000e+00], [ 1.00000000e+00, 1.00000000e+00, 1.00000000e+00, ..., 1.00000000e+00, 1.00000000e+00, 1.00000000e+00], ..., [ 7.20289280e+07, 1.78018800e+08, 2.78123104e+08, ..., 2.78123104e+08, 1.78018800e+08, 7.20289280e+07], [ 6.04602560e+07, 1.65738784e+08, 2.66663328e+08, ..., 2.66663328e+08, 1.65738784e+08, 6.04602560e+07], [ 5.06574920e+07, 1.51781760e+08, 2.54213152e+08, ..., 2.54213152e+08, 1.51781760e+08, 5.06574920e+07]], dtype=float32), measure=area, standard_name=None, units=Unit('m^2'), long_name=u'area of T grid cells', var_name='tarea'), (1, 2)]] != []failed to concatenate into a single cube.```The `mip_convert.cfg.seaice` file is attached.
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Start with the attached mip_convert.cfg.seaice configuration and reproduce the SIday conversion for the sisnthick variable. Investigate the reported CellMeasures difference and verify that the conversion completes without the failed-to-concatenate error.

Written by the indexing model from the issue text.