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 INFRONT of the core, after a certain distance gravity modules behaves accordingly to the report above. Does not seem to be happening behind the core or depending on the center of mass.