Sometimes, after placing the bomb in the fuel dump mission, there is just the message about that the bomb has been placed, but the gate does not blow up at the next turn change. This seems to be random, I've seen it blow up other times too. Attempting to place the bomb again doesn't produce another message about bomb being placed and does not blow up the gate either. Given that there seems to be a new mission objective that aliens have to occupy the space in front of a fuel tank for some time this may be a huge problem.
However, aliens didn't seem to stay long enough in the respective area and/or perhaps I was fast enough with killing them anyway. I did it with sniper throughwall shots and grenades. I had a lucky starting situation, only 6 aliens and 4 of them spiders.