I’ve placed a flare object, but its not showing, either in-game or in editor.
I actually had that too, it was the same thing when i reinstalled, and it also started randomly deleting my scripts. so i emailed them, but they never responded to that issue.
I reinstalled, and updated to 2.6 and got it working again…
that worked 
i’ve tried that already, didnt work…
Have you added a flare texture in light setting ?
yes
place the sun light over your terrain and make sure that Flare Flag is checked in camera settings.
It should work.
Check out this thread: