I can’t reproduce this.
Under hotkeys, you can filter by assigned only.
I suggest looking in your hotkeys and make sure you didn’t map Shift+space to something.
Then check your OS hotkeys too. Although in MacOS it shouldn’t be possible to map that.
Check for any apps that might control hotkeys and snippets. Like BetterTouchTool, Alfred, Espanso, and all those types of apps.