Keychain passwords disappeared

I use an iPhone, a Mac Book Pro, and an iMac. Keychain is on for all of them and I did not have any problem so far. Today I logged in my iMac and my apps complain that they cannot find the password. So I went to keychain and realised that all the passwords kept there dissappared. Then I go to my iPhone and there I see that the passwords are there. I searched the communities a little and a couple of suggest that turning off and on the keychain on their iPhone helped. I have several questions:

1. Why am I having this problem?

2. Why turning off and on keychain on iPhone would help?

3. If I turn off keychain on my iPhone, is there a possibility to loose all my passwords? Where are the passwords actually kept? On iCloud, I do not see a keychain app or something.

4. What are possible other solutions?

Any swift response would be very much appreciated.