If your PK XD friends list vanished overnight, the game may simply not be showing it because of a sync glitch or bug, especially after updates or connection issues. This is a common type of technical problem in PK XD where features can temporarily disappear.
Try restarting the app, updating it to the latest version, and logging out and back in to force a refresh, as servers sometimes take time to sync social data after an update.
Also check the Friends menu (two-heads icon in your in-game phone) to see if requests or accepted friends still appear there — if they do, your friends are not gone, just not loading correctly.
If the list remains empty, you may need to re-add friends manually using their exact username and send new friend requests.
Do you have another way to solve it? We'd love to hear from you in the comments.