There has been a problem with VH bases for some time now. I thought it would be fixed by now but it isn't.
When the north most hanger is down, upping a tank or osty from the base becomes nearly impossible. You spawn on top of the hanger, then roll off and end up upside down.
If there are supplies out, sometimes you can take one and get righted up.
Also, if you just up, then someone kills hanger within a second or two, you end up on top of the destroyed hanger. (happened just now to me)
Effectively, all you need to do is take down one hanger, the north most in question, to shut down defence at any VH base.