Anki automatically switches from "Decks" view to card when it is left open overnight

[abdo]

This is actually intended.
Related post: Review opens during card creation - #7 by abdo

@EliasZ

And I wonder if this affects the time statistics of my cards. Sometimes I’ll be working on other stuff on my laptop, and Anki will be sitting in the background, showing a card, when I would expect it to show the “Decks” menu.

It doesn’t affect your stats, except for the logged answer time of the shown card if you answer it after you came back to Anki. You can simply avoid this by switching to the main screen then back to the review screen.