I found a bug :
VS 2019.16.10.0 / Telerik 2021.1.218.1
strangely, I had functionalities that disappeared in my grid "group" and i found how to reproduce the problem :
In radgrid, from designer :
1) open property builder and add columns.
2) get a column and add it to group panel.
3) uncheck group panel check (example because must in group but user must don't touch it and can't add)
4) in columns, column added to group, uncheck "isVisible".
5) bind datas for example.
run project : Ok works.
now Open again property builder, rename not group column header, click Ok.
save, run project : group disappeared, if you go in designer group descriptors : all is empty.