I have a link to a repo thisRepo with commit id : https://github.com/user/thisRepo/tree/<commitid>. When I use github to view the repo at this commit, I see

I am trying to access the repo at this commit point using.
git checkout <commitid>, I get fatal: reference is not a tree: <commitid>

Just to add I have done git fetch for all branches for this user, after adding it to my remote. I am able to access other commit.