I got new update on this issue.
I think it is caused by `(clojure-find-ns)`.
Here is my found:
I created a simple clojure project for used by all org-babel-clojure src
blocks.
```elisp
(progn
(find-file (expand-file-name
"~/.emacs.d/Org-mode/ob-clojure/src/ob_clojure/core.clj"))
(cider-jack-in))
```
I edebug the `org-babel-execute:clojure` process,
`org-babel-execute:clojure' has a step: ~(clojure-find-ns)~ .
This is from ~clojure-mode~. It will find current clojure buffer
possible clojure namespace (even in org-mode). When I the following
example org-mode buffer, it will return "namespace-not-found" error in
nrepl response dict. Then src blcok has no error, not results.
```org
#+BEGIN_SRC clojure :session
(in-ns 'user-kk)
or
(ns user-kk)
#+END_SRC
#+BEGIN_SRC clojure :results output
(print "hi")
#+END_SRC
```
Here is a part of function `clojure-find-ns`:
#+begin_src emacs-lisp
(when (or (re-search-backward clojure-namespace-name-regex nil t)
;; Or any form at all.
(and (goto-char (point-min))
(re-search-forward clojure-namespace-name-regex
nil t)))
(match-string-no-properties 4))
#+end_src
So I created an PR to disable find namespace in Org-mode buffer:
https://github.com/clojure-emacs/clojure-mode/pull/465
