Dock disappearing on boot

Sometimes after boot, everything loads except the Dock doesn't show up. It's easily solved by command+option+D a few times and is not a big problem, but I wonder if anyone else here has this issue, is it common, what could be the causes, and how to debug it?

I tried deleting Dock preferences and removing some apps from startup, but not everything. The suspects are some other startup apps, but I wonder why would they cause such issue. It doesn't help that it only rarely doesn't show up (maybe 1 out of 10 boots).

Sierra 10.12.5, 1060 GPU.