Check the (invisible) collision box of your HV. Especially if you have a mining turrets sticking out somewhere this can make the collision box (which seems to be like one big rectangle sometimes) of your HV so big that some/all of the drills are incapable of ever hitting the dirt…
Also I noticed that drilling on the server is very unresponsive compared to singleplayer.
Also had problems with camera not being aligned to center (bad screenshot but sometimes it’s clearly visible):
https://s27.postimg.org/bly1vjwgz/20161228163856_1.jpg
Relog fixes it.