> Looks like it was introduced with:
>
> f5573e6a0 org-capture.el: Fix heading's level when inserting a
> template "here"

I believe the issue is due to `org-back-to-heading' moving point 
when calculating the heading level.
The attached patch corrects the issue on my end.
Tested by running:

#+begin_src emacs-lisp :lexical t
(dotimes (n 3)
  (let ((org-capture-templates
         `(( "e" "test"
             entry
             (file "/temp/null.org")
             ,(format "* %d" n)
             :immediate-finish t
             :no-save t))))
    (goto-char (point-max))
    (org-capture 0 "e")))
#+end_src

With a buffer containing:

* foo
** one
*** two
**** three
*** four

Which results in:

* foo
** one
*** two
**** three
*** four
*** 0
*** 1
*** 2