We have had players with a similar issue, missing towers. Not exactly the same but ill provide the steps that were taken to resolve the issue.
-Remove tower(s) and place them on storage (in this case I guess remove dragon and leave it be)
-Change your avatar portrait to any other portrait you have in your gallery.
-Force-restart the game
-Return tower(s) to their respective postitions or any island you wish (in this case put the dragon back on the perch)
-change your avatar portrait back to what it was
-do a final force-restart
Hope this helps, it was given by PG support team.