When the user groups by a column, the grid makes an AJAX request.
If that request returns data that is grouped differently than the "current" state of the grid, the grid crashes (see attached images for the crash location and call stack).
Even if the server returned incorrect data, it would still be nice of the grid not to crash, but to fall back gracefully.
But in our particular case, this is NOT cause by the server returning incorrect data.
Instead, it is caused by the grid itself, in connection to another issue we have submitted recently
If the user is quick enough to change the grouping arrangement several times in a row - say, quickly remove all groups one by one, - the grid initiates a request when the first group is removed and does not drop it when the second group goes away.
Therefore, by the time the first response from the server (containing all groups but one) comes, the user has already removed all groups, and the grid crashes.