I never had a problem with this autosave beachball thing in the years since Nuendo 3.
I recently disastrously updated to Yosemite and had to go back to Mavericks via the Time Machine backup, it is only since this, I have the slow save problem and also I have parallel drum compression busses which are now phasey.
If this gives anybody any ideas - please post them up as soon as poss. I’m so gutted I’m right in the middle of tonnes of work and this is really slowing me down!