I have been experiencing similar problems in my app. Various Windows 10 users of my app have been reporting container controls missing from windows in the app. Problem is, not all users are reporting the same controls missing. Also, my version of Windows 10 is showing all the controls. So, I can't readily produce anything to demonstrate what is being reported. Also tough to fix because I can't reproduce the problem they are clearly demonstrating to me via screen shots.
I use a container control to create a lookup field for my database app. A user will start typing in a text field and a listbox will drop down below the field to allow the user to select an entry based on what they are typing. When the user selects an entry, the listbox disappears. The text field and listbox are in a container control that may or may not overlap controls below the text field. When there is no typing, the listbox is not displayed, but that space is used for other controls.
When I first encountered this problem after using 2018r2, I "fixed" it by dynamically changing the height of the container control. Instead of having a container control with a height of 150 to accommodate a text field of 22 height and a listbox of 125 height below it, I would instead have the container height be 23 and toggle it to 150 whenever I wanted the listbox to show. This works most of the time.
Below are screen shots sent to me by a user who at first could not display the control at all in Windows 10, but did have some success by running the app in Windows 8 compatibility mode.
The first image shows the bottom of the text field missing. At least with part of the control showing, he was able to give it focus and type in it which then displayed the listbox selection control. Again, just running in Windows 10, nothing was showing so he could not get focus at all.
This feature in my app has been working fine for years and not experiencing any problems until 2018r2. I'm not saying the bug is in 2018r2. What I am saying is I'm not understanding how to adjust my code to make it work for 2018r2.