If you are experiencing unusual tabbing order in your form then, it must be because you are creating a multi-column form.
In multi-column forms, how you add the rows will affect the tabbing order.
If you add the form rows like this,
Then, the tabbing order will be this:
How to Fix this Issue?
To fix this issue, you need to use the Add Row option in the form builder to add rows.
After you Add Rows, you can add the form fields.
Now, the tabbing order in your forms will go like this: