Before I even started producing satellites, I got the orange pause-popup saying I launched a rocket without a satellite. I was at the other end of the factory, there is 0% chance of my launching it by accident, and when I ran to the silo it just started building a new rocket, the checkbox still ticked.
Obviously, the silo should've waited with a rocket up and ready, until a satellite was inserted in. Instead it just launched and wasted the materials.
As I tried to reproduce the bug on the next "cycle", I found out that the rocket launches because an inserter puts processing units into the rocket inventory. The rocket launches because it's inventory has something in it - but it's not the satellite, so you get no reward.
No mods are involved.
All in all, the bug is that inserters will insert processing units into rocket inventory. The auto-launching feature doesn't recognize for the content of the inventory since it's only meant to accept satellites, and launches without a satellite.

I have attached the save file. If left alone, the rocket will momentarily auto-launch without a satellite.