Did Unity changed some part of Transform system after 5.6.2?

Hi guys,

I'm currently working on a dynamic city system, which moves buildings around and active/deactive them base on their visibility. When I was using 5.6.0, it's all great, I can run a 6km * 6km size city inside editor at 200FPS. But I cant remember when(most likely 5.6.1P4), things got changed. Editor freeze for a little frame whenever a building is active(however the fps showed in stats of game view never drops..), and this is editor only, everything is good in a build player.

I admit that the each one of these building prefabs contains tons of gameobjects, which is bad and needs to optimized. But I cant understand why this happen only after 5.6.2 and its getting even worse in Unity 2017. I've read some post about unity is optimizing its transform system, could it be possible that the new transform system(or hierarchy view?) inside editor have problem of handling complex transforms?

The project is to big to upload for a bug report. Is there anyone who had the same issue or solutions.?

In the attached files,
1.png shows the hierarchy of one building prefab.

2.png shows how the viewculling is working. It's actually not much alive buildings at one time.

3.png shows the fps inside editor. however, it's incorrect...because when ever a new building is active, it freeze..

 

@karl_jones
Can you elaborate on what changes were made in 5.6.2? Coz I see "setParent" taking a lot of CPU while profiling in 5.6.2. Though the game was upgraded from 5.3.x recently so not sure when exactly that change happened, probably need to re-test in 5.6.1(0).

 

So after spent one day tring to reproduce the bug in a new project, no luck. Seems the only way to show you guys the bug is to upload my current project.
There is also another editor only bug that blocks resource.loadasync from finishing and cause lags whenever resource.load is called after switched levels(two same resources, load very fast in the first scene, and caused a huge spike when load it after level switched, and loadasync never returns success unless another resource.load is called) . I've tried to reproduce it in a new project month ago, I've managed to reproduce that in the first place but It just gone and never showed up when I'm ready to submit....
Two bugs combines...the development process is like hell..
So could you give me more detail about where to upload my project? Thanks.