I created on our dev environment a cluster using the shared access mode, for our devs to use (instead of separate single user clusters).

What I notice is that the performance of this cluster is terrible.  And I mean really terrible: notebook cells without any action, so just dataframe definitions take minutes to complete.  Even though nothing has to be computed (lazy computing in spark).

When I disable shared compute (so change to single user), performance is reasonable again.

Any ideas?
At the moment I am the only user using the cluster, so it can't be the cluster load.