Please also take into account that the changes will be saved in the Change Log only if they were made not directly into the DB (for example changing this field via SQL script won't be shown in the Change Log) and also, you need to save the record every time a change is made.
So for example, if you change Mobile phone field to 999999999, then to 888888888 and to 7777777777 without saving after each and every change - it won't appear in the change log.
I am changing the record and saving it every time. It does not show all the changed values in Change log. It is showing only very first entry in change log. What would be the issue? Did you try to replicate it?