P: Photoshop hangs when using smart objects

It's no bug with the GPU. All other programs are working properly and my drivers are always pretty much up to date. But I can try to install the latest drivers. However I doubt that this will solve the problem. 

Well, fiddling around with the performance is always necessary because IF disabling GPU stops the hang (freeze, crash, whatever), this is a bug with the GPU and you need to contact the manufacturer to see if there's a newer driver for it. 

Photoshop doesn't crash it hangs or is stuck forever. And I can't reproduce the issue, it happens occasionally. So fiddling around with the performace settings isn't really possible as it would affect my performance while working and that's not really an option. I was rather hoping that this is a known issue and somebody had a solution for it.

When Photoshop crashes (actually crashes), this is the first thing to do, try resetting your Photoshop preferences. Press and hold Alt+Control+Shift (Windows) or Option+Command+Shift (macOS) immediately after launching Photoshop. You will be prompted to delete the current settings. You can also reset preferences upon a quit if Photoshop is running by going into General Preferences>General>Reset on Quit.

(macOS only) Open the Preferences folder in the Library folder*, and drag the Adobe Photoshop CS Settings folder to the Trash.

This action only affects the items found in the preferences dialog box. Numerous program settings are stored in the Adobe Photoshop Preferences file, including general display options, file-saving options, performance options, cursor options, transparency options, type options, and options for plug‑ins and scratch disks. Brushes (and lots of other setting) are not affected by the above instructions for deleting preferences. You may wish to make a screen capture of the settings in the Preferences dialog to reset them prior to deleting of this file.

Also: https://helpx.adobe.com/photoshop/using/preferences.html

*To manually delete Photoshop preferences:
Quit Photoshop.
Navigate to Photoshop's Preferences folder:
macOS**: Users/[user name]/Library/Preferences/Adobe Photoshop [version] Settings
Windows 10: Users/[user name]/AppData/Roaming/Adobe/Adobe Photoshop [version]/Adobe Photoshop [version] Settings
**Note:The user Library folder is hidden by default on macOS. In the Finder, hold down the Option key when using the Go menu. The library will appear below the current user's home directory.
Now you can drag the entire Adobe Photoshop [Version] Settings folder to the desktop or somewhere safe for a backup of your settings

If that doesn't fix the issue:
Go to Preferences > Performance... and uncheck Multithreaded Compositing - and restart Photoshop.
Still crashing? 
Go to Preferences > Performance... click Advanced Settings... and uncheck "GPU Compositing" - then restart Photoshop. Still crashing? 

Both. In most cases it hangs for about 5 to 10 seconds - especially when I drag smart objects from one file to another. But it also happens that is hangs for eternity (with the GPU running at a high load) and I have to kill the process.

Hangs meaning the application actually freezes or it stalls for a few seconds then continues???

Can you go to Photoshop Help Menu>System Info and copy/paste the details here?

It will help to investigate the issue.