Find out what process registered a global hotkey

One possible way is to use the Visual Studio tool Spy++.

Give this a try:

1. Run the tool (for me, it's at C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\Tools\spyxx_amd64.exe)
2. In the menu bar, select Spy -> Log messages... (or hit Ctrl + M)
3. Check All Windows in System in the Additional Windows frame
4. Switch to the Messages tab
5. Click the Clear All button
6. Select WM_HOTKEY in the listbox, or check Keyboard in Message Groups (if you're OK with more potential noise)
7. Click the OK button
8. Press the hotkey in question (Win + R, for example)
9. Select the WM_HOTKEY line in the Messages (All Windows) window, right click, and select Properties... in the context menu
10. In the Message Properties dialog, click the Window Handle link (this will be the handle for the window that received the message)
11. Click the Synchronize button on the Window Properties dialog. This will show the window in the main Spy++ window treeview.
12. On the Window Properties dialog, select the Process tab
13. Click the Process ID link. This will show you the process (In my Win + R case: EXPLORER)