Cannot locally 'sync-all get'

Like so often, ./sync-all pull failed today in my local clones, first with "... not on a branch", after sync-all checkout master, with "fatal: Reference ... not a tree". (Aside, that nonsense didn't happen before the introduction of submodules.) The usual remedy is rm -rf ./clone git clone ./ghc ./clone cd clone ./sync-all get but today it failed with

Klone nach 'libraries/xhtml'... Fertig. Unterprojekt-Pfad: 'libraries/xhtml': 'fb9e0bbb69e15873682a9f25d39652099a3ccac1' ausgecheckt fatal: Projektarchiv '/home/dafis/GHC/./haddock.git' existiert nicht. Klonen von '/home/dafis/GHC/./haddock.git' in Unterprojekt-Pfad 'utils/haddock' fehlgeschlagen git failed: 256 at ./sync-all line 123.

Any idea what's up? Cheers, Daniel