Linux repository size exploding

I have a linux source code repository on gitlab with several branches that is exploding in size and i can’t find out why.

According to the usage quota page the repository currently has 28.8 GB and 1.3GB CI artifacts. However when I do a full clone with all branches and tags with git clone --mirror the resulting local copy only has around 2.3 GB which is around the size i would expect.

What can i look out for to find what is eating away the GBs?