When FixedColumns and RowGroup are both enabled, there is an error that comes from FixedColumns code:
Uncaught TypeError: Cannot read properties of undefined (reading 'anCells')
There have been posts about this issue before (one, two as a sample), and the answer on those threads was that FixedColumns and RowGroup are not compatible per the compatibility matrix. The current matrix now indicates that the two should be fully compatible, but the same error still exists.
To see the error:
1. open this test case
2. open the browser's console
3. rerun the sample and you should see the error in the brower's console
4. note that the rendered DataTable, when scrolled side to side, doesn't fix the left columns
Is the compatibility matrix wrong or is there a bug with FixedColumns?
(As an aside, FixedColumns 'left' and 'right' options don't seem to be working properly which is evident on FixedColumns own example pages here and here. Workaround: use deprecated settings 'leftColumns' and 'rightColumns')