Ok so I am going to try to be as specific as possible with this because it just happened again.
The first time it happened I was using I think a BA A320 taking off at stuttgart airport, when I reached V1 speed the plane clipped through the ground and continuously fell into it.
The second time wich was just now, I was using a Cessna 208 Caravan, spawned in at grand canyon national park and Immediately clipped through the floor.
If you need it I’m using a 5s and the latest OS (11.0.3 I think it was) I have also noticed this bug with jets, when you drop from a really high altitude then suddenly pull up, your jet freaks out and glitched into the floor.
Hope this was helpful feedback and I hope you can locate this bug