I know that my gains come in waves. I get a great size then I have to break. During my break the swelling and most of the gains disappear. At the end of the break what’s left is the permanent gains. I know I have permanent gains because when I start back up again it’s bigger than it was before. I would say that you didn’t loose all your gains, just most of it went away. Once you start back up those gains will reappear.
It’s almost like the permanent gains I have now were the pre-break gains I had a few months ago. Just keep it up and it will grow on top of previous gains. Only measure once a month or so to see your true gains.