I have seen that my Backlinks are disappearing from 40+ they when down to 10, I am not the one submitting the backlinks, and when I ask the person that its doing my SEO about it, here was his answer

"Regarding the Backlinks , they are added or removed as Google crawls the previous links that were added two-three months back and if google does not find the links there, it removes it so it is a regular process, it goes up and down."

its this true? because I been using the same tools to check the links on my other websites and I dont seen changes on the quantity of my others sites

please any clarification with this will be appreciated