If u have a large ship (or part of a station) and walk far away from the core (~560m in my case),
the gravity of the Gravity Unit get neutralised and if u try to get in gravity with a new Gravity unit (placed also ~560m away from the core)
you get in gravity again, but only for a few seconds and then gets neutralised again.
Havent tryed this at a station yet.
Edit:
How to reproduce:
Core + structure stretching a few hundred (300+) blocks comming of the core, after a certain distance gravity modules behaves accordingly to the report above. Does not seem to be depending on distance to center of mass.
The distance of this effect (to the core) is depending on the structure (a structure stretching in the opposite direction changes the border of this effect)