Can you explain that in more detail? All your journal entries? That is hard to believe as Diarium doesn't just delete all data and doesn't handle that keyboard command either.
Can you explain as detailed as possible what exactly happened when you pressed that key combination? Did the app go to another screen? Did the app close? What is "Diarium OS+ version"?
In order to just bring an entry to another date, you can click on the date-field on the top of the window