Let me rephrase your question:
I start drowning when I go into a Build Gate or the Tutorial Island Portal.

This is most likely caused by lag. Just wait there for a few more seconds and you will most likely teleport. I have never seen an instance where someone has drowned in a Build Gate or the Tutorial Island Portal.

 

You can't die at spawn as invincibility is set to true. The bubbles will show but that it because stargate is lagging but you shouldn't be in the portal so long that you die from drowning.