Problem description I've observed a disconnection of a single Diffusor from Flexible Duct while promoting the view.
Solution
Whenever you observe the incorrect representation of Flexible duct in Single-Line promoted isometric view use the key-in: MDL COMMAND DVREFRESH
For example, the Semi Flex duct is not displayed correctly in the first instance in the Promoted view while using drawing seed Mech – Mechanical Plan – Single Line. Please refer to the below image.
>> Normal View
>> Promoted View
When changing the view orientation such as from Iso to Front after applying the view, you need to clear the cache to recreate the graphics by using the key in: mdl command dvrefresh.
Please see the video below showing the same workflow for better reference.