Saving Animation Controller randomly alterates the file

Questions & Answers
1

Whenever I do a small change on an Animation Controller or just save it because I want to be sure, the diff looks like this:

[-] m_Controller: {fileID: 0}

[+] m_Controller: {fileID: 9100000}

…

[-] m_Controller: {fileID: 0}

[+] m_Controller: {fileID: 9100000}

…

[-] m_Controller: {fileID: 0}

[+] m_Controller: {fileID: 9100000}

…

Now after comitting and saving the Animator again, it changes back to fileID: 0.
I don’t know what m_Controller: {fileID: …} means. What do you think causes this?

2

Same question here: https://forum.unity.com/threads/saving-animation-controller-randomly-alterates-the-file.469070/ At the time of writing - WITH NO RESPONSE. Bump