The account I was playing with has disappeared from the login list.

The account may have been hidden due to the "Remove Account Record" action.
Please try the following steps:
■【Apple】 I keep getting switched into a guest account at 5:00 AM.

If you were playing on a Guest Account:
If you are currently logged in with a different account, open the User Center from the "User" icon at the top right of the title screen and tap Switch.
In the User Center, under Other Login Methods, select Sign in with Guest. This will restore the account to the list.

If you were using a Linked Account:
If you are currently logged in with a different account, open the User Center from the "User" icon at the top right of the title screen and tap Switch.
Under Other Login Methods, select the service you used to link your account and log in. The account will then reappear in the account list.

Please note: Selecting Guest Login or deleting an account during the switching process will create a new account and start the game from the beginning.