Cellar C2 is having issue with time sync. It may result with a "ClockTooSkewed" error when you try to list or access files.
We are working on fixing the clocks on the Ceph monitoring servers. (Ceph is the software we use to provide the Cellar service.)
EDIT 12:40 UTC+1: One of the reverse proxies in front of the Cellar system was desynchronized. This proxy is now out of the pool for further investigation and the issue should now be fixed.