Sure, In my original post, if we see, in a case there is a table Unit and I clicked on add record, there there is ONLY a table Brk1List with add button in which I added a record and for second record I got error.
In my Updated reply, in a case there is a table Unit and I clicked in add record(this part is cut from the video) and there we can see a text input field Category along with the table Brk1List that was present before. Now, I am able to add multiple records to Brk1List without any error.
The issue is, we cannot add more than one record to Brk1List if there is no text input field present parallel to it. If I remove that text field now, I again bump into same error.