Hi, Masss and thanks for your support!
SMC is designed that way.
If you want to keep the ID you could do the following:
When scheduling a conference, go to Advanced Settings and set the conference as Active Conference.
If you set the conference as Active, you will have to define a Conference ID, which will not be modified even if you make any modifications (ex. Add new participants) to the conference.
Below you can see exactly what Active conference does: