Unmanaged RAP BO with draft: error when pressing edit

I have implemented Unmanaged RAP BO with draft on BTP ABAP trial environment. OData version is V4.

unmanaged implementation in class zbp_i_person_u unique;
with draft;

Create operation with draft went successful however, when I press "Edit" on the detail screen, the following error is issued.

With debugging, I found that the error had occurred at process related to locking.

The failed structure got "NOT_FOUND" error as below.

I haven't written my lock logic yet, and the implementation is almost empty as below.

  METHOD lock.
    if sy-subrc = 0.
    endif.
  ENDMETHOD.

If I disable draft and switched to OData V2 (because with V4 we don't see Edit button without draft), there's no error.

Is draft with unmanaged BO not supported?

Regards,

Mio