I may have done something silly with git. I removed files from the repository, erasing their history, with such command: git filter-branch --tree-filter 'rm file' HEAD. Then, after committing, when pushing the results, there was conflicts because it says that i haven't got the newest state of my branch. So, without knowing what to do (i'm very new to git), i forced the push. And everything went fine after.
But when i was on the web page of my repository, i clicked on the last commit, to see what it contains. After some time, a page written "500, Something went wrong" appeared. When i clicked on a other commit, it displays the correct results.
So i think that what i've done, with my forced push, is not handled by the web user interface, and leads every time to an error.