On PC coop, engaging a tank or harvester over 200 m seemed to make their rocket and machinegun projectiles not render, making you not take any damage. Their firing effects could be seen but any bullets or rockets just disappears.
If you move within 200m, the rockets and explosions magically reappear and you start taking damage.
I don’t think it’s a bug, instead, i think this is intended feature.
Each machine in the game has certain range of their weapons but machine weapon range is always shorter than the view distance at which range you can see them.
For example:
If machine weapon range would be equal or greater to the range you can see them, then that can lead into situations where machines fire at you as soon as they appear on your screen or even before appearing. That wouldn’t make the game fair, wouldn’t it?
Yes i understand that… but its feels like a bug… since they just sit there and constantly attack you and many areas have large stretches of open fields.
If they have limited attack range, the Tank/Harvester AI should always advance to attack/keep you in range like the rest of the Machines instead of just sitting them and lobbing blanks and only to have explosions suddenly appearing around you and dying when you ran up closer…
They used to do that but latest update skewed the machine AI. 
Most notable in the accuracy and firerate of the harv/tank weaponry.