If the bounds of the ISM actors are bigger than a single cell they might be getting promoted to a higher level streaming cell, which is bigger and covers multiple tiles. You should check the debug streaming grid overlay to see better what is happening.
To turn on debug streaming grid: wp.Runtime.ToggleDrawRuntimeHash2D
- It shows level 0 by default, you can change the grid level with
wp.Runtime.ShowRuntimeSpatialHashGridLevel <level_number> - You can also show multiple grid levels at once with
wp.Runtime.ShowRuntimeSpatialHashGridLevelCount <level_count>
Hope this helps you see what’s happening.