Main reason that happens is that the game or app is running with higher privileges than DDM. In a typical Win10 RedStone system, DDM will size "Windows PowerShell" but not "Windows PowerShell (Admin)"...

If your game(s) require admin privileges, close DDM and restart it with the "Run as administrator" option.

I should have thought of that...thank you, I'll give that a go. Appreciate it.

Thank you for the suggestion, but this did not work. Not sure what's going on.

This is getting super frustrating. Dell Tech Support wouldn't help me and I really don't want to return this monitor but I'm about ready to.

I understand that yes, but it's literally every single PC game I've tried, all which can run in windowed or fullscreen mode. D3, for example, or Heroes of the Storm, Destiny, Overwatch etc. Like I said, I got it to work one time where DDM recognized the game window and resized, but it literally would not the next day.

I'm sure you realize that you can't window a game that runs fullscreen. The window the game runs in has to be sizeable (using the window borders) to be resized by DDM. Can you provide the name of an app or game that won't resize but should?

I checked D3 and don't see any problem, even though D3 doesn't have a normal size/system menu: as long as its in windowed display mode, DDM sizes the D3 window to the Easy Arrange (EA) cell size. 

The only thing I can think of is if you are running Win10 with virtual desktops (VD), and EA is disabled on the VD you use for gaming. DDM allows you to have different EA settings for each VD, so it is possible to have EA enabled on, say, VD #1 and disabled on VD #2.

You should also, of course, make sure you have the latest version of DDM, which is b.1899.

Swamp I want to thank you for working through this with me. I will remove everything and start from scratch when I get home. Not running any VD's any longer but if you're getting it to work then something's got to be wrong with my setup.

I'll post my progress tonight.

Thanks again.

Progress. The EA now works in everything except 1 game, and I am not sure what makes this game different.

I had similar experience but with Visual Studio 2017.

I have to run VS as administrator and, just like @Dieselblues' game, DDM's 'Easy Arrange' wasn't allowing VS to snap or resize to any predefined window.

However, when if I set VS to run without administrator permissions, VS did snap and resize as expected proving VS was overriding DDM settings.

Following @swamped207 suggestion,  to allow VS to run 'as administrator' AND have it snap to DDM windows was to have DDM run as admin too.

To change DDM to run as administrator:

1. Close DDM completely.
2. Open file manager and browse to location of ddm.exe, C:\Program Files (x86)\Dell\Dell Display Manager.
3. Right-click ddm.exe and select 'Properties'.
4. Click 'Compatibility' tab.
5. Check the option to 'Run this program as an administrator'.
6. Click 'Apply'.
7. Click 'OK'.
8. Restart DDM

Everything now works like a charm. Or so I thought - Now DDM wont run at windows startup because it is running with elevated permissions.