can't checkout ghc 8.6 branch correctly -- something wrong with transformers mirror repo?

Hey everyone, whats wrong with the 8.6 branch? when i do a fresh clone, i wind up with this error : $ git submodule update --init --recursive error: Server does not allow request for unadvertised object def8c55d0c47c1c40de985d83f052f3659b40cfd Fetched in submodule path 'libraries/transformers', but it did not contain def8c55d0c47c1c40de985d83f052f3659b40cfd. Direct fetching of that commit failed. 14:17:43 ~/D/r/ghc-8.6.5-series (ghc-8.6|✚6) $