Currently those 2 shortkeys are both used for the same command. (version 969)
In my Firefox those 2 shortkeys are different:
Ctrl+H - lets me to toggle a pane of history - Recent Items (Sorted By Last Visited)
Ctrl+Shift+H - opens a window of History
I think in a similar way in Everything it will be the history of the Run/Opened items and the history of the searches typed.
I found these threads to be related:
viewtopic.php?f=4&t=6116
viewtopic.php?f=4&t=6457
I edited my Ctrl+H shortkey to trigger - Recent Items Bookmark
Ctrl+H and Ctrl+Shift+H
Re: Ctrl+H and Ctrl+Shift+H
(LOL. Where did that come from? I've never seen it before .)