When the grid is configured for InCell editing and frozen columns, it is expected the first editable cell to be opened for editing when a new record is added. 

However, when there is not an editable cell in the locked columns, it would not search in the main content. Here is an example:

https://dojo.telerik.com/ucEraQOW

A temporary workaround would be to override the editModel function and check in the second table as well:

https://dojo.telerik.com/aJEsAnud