View modes are stuck on default view
This seems to be an ongoing issue as there are reports of other modules conflicting with the display suite view modes feature. For some it had to do with Panels as seen here:

https://www.drupal.org/node/1919452


  Posted by drupalstrap on February 17, 2013 at 5:57am Greetings,
  
  The only view mode i am able to use is the default view mode. As long
  as I am using the default view mode, I can switch layouts without any
  problem. If I try to switch to another view mode, it still uses the
  settings of the default view mode. I have tried every way of
  troubleshooting that I can think of including changing themes,
  altering CSS files and tpl.php files etc in order to try to isolate
  the problem. Furthermore, i am not able to apply wrapper or class
  styles via the UI settings. They don't appear in the source code.
  
  Anyway, I have been battling this for two days now and figured I would
  see if anybody out there has any suggestions. On the server side, I am
  using php 5.3 with apc. I have tried clearing cache hundreds of times
  as well as restarting the server to see if there was something in
  memory that was stuck. I have also tried other browsers so it is
  something related to my development environment I guess. LAMP???
  Please help. Thanks.
  
  Upload new files Comments  billsdesk’s picture Comment #1billsdesk
  commented 2 years ago I am having the same problem. I created a view
  mode and set it as the view mode to use when I edited the page. Yet,
  the Full Content mode is always used, and not the specified view mode.
  The Manage Display tab always opens the correct view mode. I turned on
  the view mode switcher, and it correctly identifies that the page
  opened in the full content mode. However, it does allow switching to
  the correct mode. I checked the permissions, and all is good. No error
  messages. I am using Drupal 7.22, and Display Suite 7-2.3. report spam
  on user billsdesk  alunyov’s picture Comment #2alunyov commented about
  a year ago Hello, I had same problem. In my case switching off panel
  for node view helped to solve the issue. I think it is something
  related with page manager. If you check settings page:
  admin/structure/ds/list/extras -> Other -> "View mode per node"
  option, in description you will find "Change view modes for individual
  nodes. A new tab 'Display settings' will appear on the content create
  form. You can also pass the name of a view mode through the URL, eg
  node/x?v=full. If you install the Page manager module and override the
  node view, Page manager will win."
  
  Added: check _ds_extras_menu_alter() in ds_extras.registry.inc. it
  explains a lot report spam on user alunyov  aspilicious’s picture
  Comment #3aspilicious commented about a year ago Status:  Active  »
  Closed (works as designed) Closing this works as designed. If you
  still have this issue and you DON'T have page manager enabled please
  reopen this one. report spam on user aspilicious  Geijutsuka’s picture
  Comment #4Geijutsuka commented about a year ago I'm having this
  problem on a new site I've been developing... The strange thing is
  that it's only happened within the last couple weeks. Something
  triggered this behavior, but I'm not sure what yet (trying to figure
  out STR).
  
  I set up a brand-new sandbox site with everything up-to-date and it
  seems to work as designed... flawless. I also don't have Page Manager
  or Panels installed, and I definitely don't want to have to resort to
  changing the view mode for every single piece of content. I'm going to
  update the problematic site (ds is up to date, but there are a lot of
  other updates) and see if that fixes it... if not, I'll be back.


In my case it wasn't panels that was causing the issue but it was due to the "revisioning" module that cause the view mode to get stuck on default. There has also been reports here:

https://www.drupal.org/node/2304917#comment-9550067

I updated to the latest revisioning v7.1.9 and it still causes issues with the view mode. The only option is to turn this off if revisioning is really not necessary.