Hello,

I believe this has to do with the recent change to #+RESULTS removal
without blank line [1]

Here's a MWE:

=====
#+TITLE: The disappearing act

* Heading 1
#+BEGIN_SRC emacs-lisp
(message "Hello")
#+END_SRC

#+RESULTS:
* Heading 2
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque et
quam metus. Etiam in iaculis mi, sit amet pretium magna. Donec ut dui
mi. Maecenas pharetra sapien nunc, ut mollis enim aliquam quis. Nam at
ultricies metus. Nulla tempor augue in vestibulum tristique. Phasellus
volutpat pharetra metus quis suscipit. Morbi maximus sem dolor, id
accumsan ipsum commodo non.
* Heading 3
=====

With point on the code block, do C-c C-c, allow running of that elisp
snippet, and the * Heading 2 subtree will get wiped out! (git just saved me
from losing data from that Org file).

After C-c C-c, you will get:

=====
#+TITLE: The disappearing act

* Heading 1
#+BEGIN_SRC emacs-lisp
(message "Hello")
#+END_SRC

#+RESULTS:
: Hello
* Heading 3
=====

My Org version: Org mode version 9.1.3 (release_9.1.3-187-g5cd7eb @
/home/kmodi/usr_local/apps/6/emacs/emacs-26/share/emacs/site-lisp/org/)


[1]:
http://orgmode.org/cgit.cgi/org-mode.git/commit/?id=1d8126385cf979cfaade0e6a82040884bd6af56b
-- 

Kaushal Modi