222(1): 名前は開発中のものです。 [sage] 2018/07/15(日) 18:42:31.42 ID:3jehjN70(2/3) AAS
2017.3のバグみたいです
報告多数ですね
外部ﾘﾝｸ:forum.unity.com

I encountered this after upgrading to 2017.3. One of my UI windows was all messed up,
so I tried to fix it, and upon hitting "Apply", some elements auto-centered.
After reviewing everything for rogue layouts or anything like that, and with it happening on other elements, I went to the internet and came across a few threads like this.
Fortunately, I saved a copy of my 2017.2 project and going back was as easy as renaming a folder.
But I think this is a pretty severe bug, it could effectively stale a project relying heavily on UI.