Extremely slow undo (minutes!)

Running Cubase Pro 9.0.30 build 266 64 bit on Mac OS 10.13.2

Take big project, select a dozen tracks, choose “remove selected tracks”, they all disappear.
Now UNDO that… Cue rainbow wheel turning for several minutes before the tracks reappear!
Depending on the number of tracks it can be over 5 minutes of idling.

I thought Cubase was frozen but it isn’t.

I have to export individual MIDI tracks and the only way I found to make sure that only the tracks I need are exported and no garbage is exported with them, is simply to delete track that shouldn’t be exported. Maybe I’m not doing that the right way, but that undo-of-death still destroys the work flow.

Halp plizz