Gitlab shows wrong repository size in admin panel


I’m having some issues with the repository statistics in my Gitlab installation.
According to the admin panel, the repository takes about 2.6GB of storage of which 77.4MB are used by LFS.
If I check out my repository, git lfs clone reports the following

remote: Counting objects: 74656, done.
remote: Compressing objects: 100% (31269/31269), done.
remote: Total 74656 (delta 40976), reused 74656 (delta 40976)
Receiving objects: 100% (74656/74656), 1.13 GiB | 77.47 MiB/s, done.
Resolving deltas: 100% (40976/40976), done.
Checking connectivity... done.
Checking out files: 100% (35688/35688), done.
Git LFS: (1587 of 1587 files) 5.74 GB / 5.74 GB

So to me it looks like there are way more than 77.4 MB of LFS used here.
If I look at the storage used by the lfs path on the server, du reports about 6.4 GB.
The actual repository directory is also larger than reported by Gitlab. According to du the repository is about 3.7GB in size (but maybe there is just some trash in the repo directory that Gitlab already ignores?)

Why am I experiencing these issues and how can I trigger a recalculation of the repository size?