Replied 31 January 2022, 6:07 pm EST
Sorry for the late response, it seems due to some technical issues this case was lost in the process. The sample provided in the above response seems to be representing the use case you have mentioned. There isn't any grouping applied initially, on applying the grouping by drag/drop columns into the group panel the restoring of grouped columns is also working fine as expected.
If you are facing any issues in the above-shared sample link then please share a screenshot/gif of the exact issue. If you have some other requirements then let us know.