Apple ID asked me to change my password

On my second phone, for no apparent reason, ‘Apple ID’ asked me to change my password!

I try to use my old password and it doesn't let me use the same password (understandable).

So I use a different password and now when I try to change it back to the old one, it won't let me reset to the password used in the past!

I have been using the same password for years and I would hate using a new password for no reason!

Is it possible to take same password again?

[Edited by Moderator]