moving thumbnails manually in Bridge does not work. After move it reverts to prior placement by file name.
Whether in folder or in collections, manually moving thumbnails does not stick.
The mentioned issue is fixed in the latest patch release #184.108.40.2063, Please install and confirm if that fixes the issue.
You can refer the issues fixed in the patch @ https://helpx.adobe.com/bridge/kb/fixed-issues.html
Ken Weissblum commented