I just recently upgraded to the latest version of Kendo UI (2021) and noticed one of my screens broke. I'm not sure if this was something that you intended on breaking so I wanted to report it as a bug. I had a screen with a grid in which the detail contained a child grid. This particular screen doesn't have a lot of rows and the due to the usage of it the detail is extremely important and I have it set to auto expand. The auto expand still works in the respect that the rows show as expanded but every row has the same detail...which is the detail belonging to the first row. Here is a dojo showing the bug in action: https://dojo.telerik.com/@bowensby/EfUMihUp.
The main place to focus is the dataBound event on the main grid. I found a workaround using the commented out lines (the .each in jquery). The original way is cleaner but it only causes detailInit one time and therefore repeats the same detail for every row.