Hi Himanshu,
This can be resolved, using microflow instead of using association.
This happens because sometimes the DG2 is not able to load the data through association because of page load.
Hope it helps!
We had a similar issue after converting.In our case, the Data Grid 2 used a microflow as the data source, and inside that microflow we had a Retrieve from database activity.
The fix for us was to remove the microflow as the data source and instead use a direct "Retrieve from database" with XPath in the data grid itself. That resolved the "Associated object should not have already been retrieved over schema" error.