Factorio Forums

So, the object doesn't get damaged.
(or, (maybe) the object get damaged only first attack)

After I hit the gun, biter starts moving.

My guess:
If the biter can see me directly, the come to me and also they go to the object and start destroying.
But if there is an object outside of the screen, the biter will be frozen beside the object.

I have seen this many times.

And I think this is intentional. They only attack a bit, but then pause. This way player is alerted that something is under attack, but they have a lot of time to react back. So they will only continue attacking and destroy things when player is close by again. Otherwise new players would be very quickly destroyed by bitters. I am not sure if that is really what it is.

It is a bug, and it should be fixed in the next release.