Diff with master (HEAD) disapeared

It seems in our project on gitlab.com that the possibility to compare the target branch with ‘master (HEAD)’ is gone… The only options remaining are ‘master (base)’ and ‘version xxx’. This possibility to compare with the HEAD of the master branch is an important feature in our code review process…

Is there the same for everyone, or is there a problem with our project (but I have other projects on gitlab.com and it seems to be the same…)? Is it temporary and it will come back quite promptly?

Many thanks!