Q u o t e:
Well all us engineer's can't seem to find any of these anymore, I have read all the "gas cloud" posts but this post is for a blue reply to let us know if this is a nerf or a bug. Please blizz a reply.

Hello everyone. i just thought I'd drop in to let you know that it has been confirmed by QA that respawns of gas clouds are not working properly at current.

This is slated to be fixed in the next patch (2.3.2).