Unloading zero unused objects (zone refresh) seems kind of silly considering it takes a long time to do so and it's seemingly good for nothing. (Memory.freeUp(385MB => 385MB, no change)
If you want to reduce the amount of objects then why not make one combined image of the map that includes all objects that are not moveable and interactable anyway? No need for permanent shrubs and other stuff that are not removeable and not animated to be an individual gameobject.
Also check the timestamps. In this example the memory freeups happens with less than 1 minute between them. Most of that minute the game is frozen. This is not always the case though. Sometimes zone refreshes are far apart.
From developer tools:
179[Violation] 'requestAnimationFrame' handler took <N>ms
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8 INFO [1] PLATFORM | 19:08:11,51 | Memory.freeUp(385MB => 385MB)
(Filename: ./Runtime/Export/Debug/Debug.bindings.h Line: 39)
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8 Unloading 0 Unused Serialized files (Serialized files now loaded: 0)
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8 [Violation] 'setInterval' handler took 705ms
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8
Unloading 0 unused Assets to reduce memory usage. Loaded Objects now: 187618.
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8 Total: 5664.700001 ms (FindLiveObjects: 64.900001 ms CreateObjectMapping: 10.800000 ms MarkObjects: 5587.100000 ms DeleteObjects: 1.900000 ms)
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8 [Violation] 'setInterval' handler took 127ms
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8 INFO [1] PLATFORM | 19:09:08,21 | Memory.freeUp(386MB => 386MB)
(Filename: ./Runtime/Export/Debug/Debug.bindings.h Line: 39)
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8 Unloading 0 Unused Serialized files (Serialized files now loaded: 0)
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8 [Violation] 'setInterval' handler took 761ms
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8
Unloading 0 unused Assets to reduce memory usage. Loaded Objects now: 187618.
80db7b0e-b7f1-4680-80a7-a5293dc7a8cb:8 Total: 6149.300000 ms (FindLiveObjects: 63.699999 ms CreateObjectMapping: 10.700001 ms MarkObjects: 6072.500000 ms DeleteObjects: 2.300000 ms)