Figured I'd add my own affirmation of a bug/issue with the grid behavior since it appears to be a similar problem.
I am having a similar issue with the DataGrid. I am using a hierarchy model as well. The main grid, when it expands a row, templates a RadzenCard followed immediately by a RadzenTabs containing 3 RadzenTabItems. One of the RadzenTabItems contains another DataGrid, and expanding a row in this grid templates another card and set of tabs.
Both grids are set up for inline editing and the elements in the tabs when rows are expanded are editable as well when the corresponding grid row is edited. Everything works fine on the outer grid, the row remains open during editing, however, the inner subgrid collapses the row when any edit is done to controls either in the grid row or in the tabs which are present in the expanded row.
I need the grids to keep their rows open during edit as well.
Please note, I did get the 2.11.17 NuGet package update which corrected the first issue you listed, but I see now that there is an update for version 2.12.1. I intend to update and see if the issue has been corrected.
I downloaded the 2.12.1 NuGet package and, from my initial testing, it appears that the behavior has been corrected. You might wish to upgrade to the latest version to see if this handles your particular issue as well.