I never had that happen but since you ID’d a recent change maybe you should temporarily disable that Waves plugin and recheck it. Just temporarily move the .dll file (or .vst file?) to your desktop and do some more testing.
Firstly, I checked the knowledge base and trashed all the prefs.
This stopped the issue of not asking to save changes but didn’t solve the load time for mix console.
I then rendered the 5 tracks, closed the programme and reopened it, no difference.
Then I disabled the original tracks, closed the programme and bingo, problem gone away.
Just to double check, I then deleted the rendered tracks, enabled the originals, closed the programe, and the original mix console load time issue is back.
I figure it is obviously something to do with the Wave GTR plug so I need to do a bit more digging.
Thanks for your ideas and suggestions Prock, I’ll let you know how I get on.