After upgrading to Apeture 3.3. I noticed that 15-60 seconds after launching it, it begings to generate 7000+ previews. It doesn't matter if I let it finish or cancel the task, with next launch of Aperture the behaviour is back. I can't stop this no matter whether I uncheck the "New Projects Automatically generate spreviews" in the Preferneces or not. I also tried unchecking the "Maintain Previews for Projects" - no change! When this behaviour starts, Aperture becomes "jerky" in response despite running it on iMac with 16GB RAM and 256GB SSD.
I updated Apeture to 3.3.1 but no change. This is seriously irritating and I am certain it only appeared with 3.3!
THANK's to all who tried to help. I would like to report that I finally deleted all Previews and Thumbnails (went to Pictures/Aperture Library - opened package content; deleted folders for Previews and Thumbnails). And started up Aperture.
Of course it went into a "frenzy" generating new thumbnails and previews (in the end my Library shrunk from 60+GB to 35GB due to new thumbnails and also lower quality setting for Previews which I defined). When Aperture claimed it was all done, I restarted it and noticed that many of my 30000+ photos had wrongly generated thumbnails (pixelated weird images or just black and white large pixels - see attached photos). When clicking on them, the correct thumbnails were generated and Aperture was busy and I had to restart it several times. You can imagine, clicking through most of 30.000+ photos takes a good part of your Sunday, but after I was done, I relaunched Aperture repeatedly more than 20 times and all it does is it keeps generating 136 thumbnails (takes about 5 seconds).
I have no idea what causes it, but I hope it is finally solved for me. If any weird behavior comes back I will report it.
I would also like to kindly ask others not to post their own issues unless they are directly related to my original post. While I want all to get help, you are far better of starting your own thread rather than hijacking someone else's. I do not mean to be rude.