An Overwatch player shares a video on Reddit of getting stuck while calling in D.Va's mech and being targeted by Sigma's ultimate. It's rather unfortunate and for the viewers, rather hilarious. It's difficult for Blizzard to prepare for every scenario and while others would call this a glitch or bug, this is just more about the wrong place at the wrong time.
This isn't something that happens every time D.Va calls in her mech while in Sigma's ultimate. That would make it a bug or glitch. This is simply D.Va rising up by the lamp, and when the D.Va mech appeared, it was too big for the space, and it made her get stuck.
And sadly for the player, the secret spot wouldn't even allow him to contest the point as the enemy team was able to use the 5v6. The Reddit post quickly derailed into discussion on whether the D.Va should be able to contest the point in the position she was in.
But it doesn't really matter as they lost the point. It would be interesting to see if the enemy team saw the D.Va in the spot and just left her there or if they just never noticed her in the first place.