Currently, when you use a GET microflow to return a list to a datagrid, if you try and use associations to display associated objects, you get these errors
As far as I understand this is intended behaviour, however it seems incredibly limiting when trying to build large dashboard displays. GET microflows are useful for data grids when you want to provide data responsively, I.E using in-page parameters. For all the fantastic things Mendix lets you do, this seems like an oddly simple limitation.
There are workarounds, such as building listviews etc, but these all miss fairly basic functionality such as searching, column ordering, default buttons etc etc that data grids benefit from.